Post-processing apparatus of solar cell

ABSTRACT

A post-processing apparatus of a solar cell that carries out a post-processing operation including a main period for heat-treating a solar cell having a semiconductor substrate while providing light to the solar cell, the post-processing apparatus including a main section to carry out the main period, wherein the main section comprises a first heat source unit to provide heat to the semiconductor substrate and a light source unit to provide light to the semiconductor substrate, the first heat source unit and the light source unit being positioned in the main section, and the light source unit comprises a light source constituted by a plasma lighting system (PLS).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.14/741,286, filed on Jun. 16, 2018, which claims the priority benefit ofKorean Patent Application No. 10-2014-0073575, filed on Jun. 17, 2014 inthe Korean Intellectual Property Office, all of which are herebyexpressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention relate to a post-processingapparatus of a solar cell, and more particularly to a post-processingapparatus of a solar cell based on a crystalline semiconductorsubstrate.

Description of the Related Art

In recent years, exhaustion of existing energy resources, such aspetroleum and coal, has been forecast with the result that interest inalternative energy resources substituting for the existing energyresources has risen. Among such alternative energy resources is a solarcell that converts photovoltaic energy into electrical energy using asemiconductor device, which is in the spotlight as a next-generationcell.

The solar cell may be fabricated through formation of various layers andelectrodes based on design. The design of various layers and electrodesmay determine the efficiency of the solar cell. Low efficiency of thesolar cell must be overcome in order to commercialize the solar cell.For this reason, various layers and electrodes of the solar cell aredesigned such that the efficiency of the solar cell can be maximized,and various processing procedures are carried out to maximize theefficiency of the solar cell. Consequently, it is necessary to provide apost-processing apparatus of a solar cell that is capable of maximizingthe efficiency of the solar cell.

SUMMARY OF THE INVENTION

Therefore, the embodiments of the present invention have been made inview of the above problems, and it is an object of the embodiments ofthe present invention to provide a post-processing apparatus of a solarcell that is capable of reducing an output loss of the solar cell.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a post-processingapparatus that carries out a post-processing operation including a mainperiod for heat-treating a solar cell including a semiconductorsubstrate while providing light to the solar cell, the post-processingapparatus including a main section to carry out the main period, whereinthe main section includes a first heat source unit to provide heat tothe semiconductor substrate and a light source unit to provide light tothe semiconductor substrate, the first heat source unit and the lightsource unit being positioned in the main section, and the light sourceunit includes a light source constituted by a plasma lighting system(PLS).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of theembodiments of the present invention will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a sectional view showing an example of a solar cellmanufactured using a manufacturing method of a solar cell according toan embodiment of the present invention;

FIG. 2 is a plan view showing the front of the solar cell shown in FIG.1 according to an embodiment of the present invention;

FIG. 3 is a flowchart showing a manufacturing method of a solar cellaccording to an embodiment of the present invention;

FIGS. 4A to 4G are sectional views showing the manufacturing method ofthe solar cell shown in FIG. 3 according to an embodiment of the presentinvention;

FIG. 5 is a graph showing a relationship between time and temperature ofa main processing process of a post-processing operation of themanufacturing method of the solar cell according to the embodiment ofthe present invention;

FIG. 6 is a graph showing a state of hydrogen based on a relationshipbetween temperature and light intensity at the post-processing operationof the manufacturing method of the solar cell according to theembodiment of the present invention;

FIG. 7 is a graph showing a state of hydrogen based on a relationshipbetween light intensity and process time at the post-processingoperation of the manufacturing method of the solar cell according to theembodiment of the present invention;

FIG. 8 is a sectional view showing another example of the solar cellmanufactured using the manufacturing method of the solar cell accordingto the embodiment of the present invention;

FIG. 9 is a sectional view showing a further example of the solar cellmanufactured using the manufacturing method of the solar cell accordingto the embodiment of the present invention;

FIG. 10 is a graph showing temperature and light intensity linesexhibiting the same output losses in an experimental example of thepresent invention;

FIG. 11 is a graph showing light intensity and process time linesexhibiting the same output losses in an experimental example of thepresent invention;

FIG. 12 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to an embodiment ofthe present invention;

FIG. 13 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to a modification ofan embodiment of the present invention;

FIG. 14 is a view showing an example of a worktable applied to thepost-processing apparatus of the solar cell shown in FIG. 13 accordingto an embodiment of the present invention;

FIG. 15 is a partial plan view showing another example of the worktableapplied to the post-processing apparatus of the solar cell shown in FIG.13 according to an embodiment of the present invention;

FIG. 16 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to anothermodification of an embodiment of the present invention;

FIG. 17 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to anothermodification of an embodiment of the present invention; and

FIG. 18 is a view schematically showing the structure of a light sourceunit applicable to a post-processing apparatus of a solar cell accordingto a further modification of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. However, it will be understood that the present inventionshould not be limited to the embodiments and may be modified in variousways.

In the drawings, to clearly and briefly explain the embodiments of thepresent invention, illustration of elements having no connection withthe description is omitted, and the same or similar elements aredesignated by the same reference numerals throughout the specification.In addition, in the drawings, for more clear explanation, the dimensionsof elements, such as thickness, width, and the like, are exaggerated orreduced, and thus the thickness, width, and the like of the embodimentsof the present invention are not limited to the illustration of thedrawings.

In the entire specification, when an element is referred to as“including” another element, the element should not be understood asexcluding other elements so long as there is no special conflictingdescription, and the element may include at least one other element. Inaddition, it will be understood that, when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. On the other hand, when an element such as a layer, film,region or substrate is referred to as being “directly on” anotherelement, this means that there are no intervening elements therebetween.

Hereinafter, a post-processing apparatus of a solar cell according to anembodiment of the present invention will be described in detail withreference to the accompanying drawings. An example of a solar cellmanufactured using a manufacturing method of a solar cell including apost-processing operation carried out by the post-processing apparatusof the solar cell according to the embodiment of the present inventionwill be described first, the manufacturing method of the solar cellincluding the post-processing operation will be described, and then thepost-processing apparatus of the solar cell will be described.

FIG. 1 is a sectional view showing an example of a solar cellmanufactured using a manufacturing method of a solar cell according toan embodiment of the present invention, and FIG. 2 is a plan viewshowing the front of the solar cell shown in FIG. 1. A semiconductorsubstrate and an electrode are mainly shown in FIG. 2.

Referring to FIG. 1, a solar cell 100 according to this embodimentincludes a semiconductor substrate 110 including a base region 10, afirst conductive region 20 of a first conductive type, a secondconductive region 30 of a second conductive type, a first electrode 42connected to the first conductive region 20, and a second electrode 44connected to the second conductive region 30. The solar cell 100 mayfurther include dielectric films, such as a first passivation film 22and an anti-reflection film 24. Hereinafter, the solar cell 100 will bedescribed in more detail.

The semiconductor substrate 110 may be formed of a crystallinesemiconductor. For example, the semiconductor substrate 110 may beformed of a single crystalline semiconductor (e.g. single crystallinesilicon) or a polycrystalline semiconductor (e.g. polycrystallinesilicon). In particular, the semiconductor substrate 110 may be formedof a single crystalline semiconductor (e.g. a single crystallinesemiconductor wafer, more specifically a single crystalline siliconwafer). In an instance in which the semiconductor substrate 110 isformed of a single crystalline semiconductor (e.g. single crystallinesilicon) as described above, the solar cell 100 may be a singlecrystalline semiconductor solar cell (e.g. a single crystalline siliconsolar cell). Since the solar cell 100 is based on the semiconductorsubstrate 110 formed of a crystalline semiconductor exhibiting highcrystallinity and thus low defectiveness as described above, the solarcell 100 may exhibit excellent electrical characteristics.

The front surface and/or the back surface of the semiconductor substrate110 may be textured such that the front surface and/or the back surfaceof the semiconductor substrate 110 have a rugged shape. For example, therugged shape may be a pyramidal shape, formed at a (111) surface of thesemiconductor substrate 110, having an irregular size. In an instance inwhich the rugged shape is formed at the front surface of thesemiconductor substrate 110 by texturing as described above, the surfaceroughness of the semiconductor substrate 110 may be increased with theresult that the reflectance of light incident upon the front surface ofthe semiconductor substrate 110 may be decreased. Consequently, thequantity of light reaching a pn junction formed by the base region 10and the first conductive region 20 may be increased with the result thatlight loss of the solar cell 100 may be minimized. In this embodiment ofthe present invention, the rugged shape is formed at the front surfaceof the semiconductor substrate 110 to decrease the reflectance ofincident light, whereas the rugged shape is not formed at the backsurface of the semiconductor substrate 110 to increase the reflectanceof incident light. However, the embodiments of the present invention arenot limited thereto. For example, the rugged shape may be formed at boththe front surface and the back surface of the semiconductor substrate110, or the rugged shape may not be formed at either the front surfaceor the back surface of the semiconductor substrate 110.

The base region 10 of the semiconductor substrate 110 may be a secondconductive base region 10 having a relatively low doping concentrationof a second conductive dopant. For example, the base region 10 may bemore distant from the front surface of the semiconductor substrate 110and more adjacent to the back surface of the semiconductor substrate 110than the first conductive region 20. In addition, the base region 10 maybe more adjacent to the front surface of the semiconductor substrate 110and more distant from the back surface of the semiconductor substrate110 than the second conductive region 30. However, the embodiments ofthe present invention are not limited thereto. The base region 10 may bedifferently positioned.

The base region 10 may be formed of a crystalline semiconductor having asecond conductive dopant. For example, the base region 10 may be formedof a single crystalline semiconductor (e.g. single crystalline silicon)or a polycrystalline semiconductor (e.g. polycrystalline silicon) havinga second conductive dopant. In particular, the base region 10 may beformed of a single crystalline semiconductor (e.g. a single crystallinesemiconductor wafer, more specifically a single crystalline siliconwafer) having a second conductive dopant.

The second conductive type may be an n-type or a p-type. In an instancein which the base region 10 is of an n-type, the base region 10 may beformed of a single crystalline semiconductor or a polycrystallinesemiconductor doped with a group-V element, such as phosphorus (P),arsenic (As), bismuth (Bi), or antimony (Sb). On the other hand, in aninstance in which the base region 10 is of a p-type, the base region 10may be formed of a single crystalline semiconductor or a polycrystallinesemiconductor doped with a group-III element, such as boron (B),aluminum (Al), gallium (Ga), or Indium (In). However, the embodiments ofthe present invention are not limited thereto. The base region 10 andthe second conductive dopant may be formed of various materials.

For example, the base region 10 may be of a p-type. In this case,materials included in the second electrode 44 may be diffused in to thesemiconductor substrate 110 to form the second conductive region 30 atan operation of firing the second electrode 44. As a result, anadditional doping process for forming the second conductive region 30may be omitted, thereby simplifying a manufacturing process of the solarcell 100. However, the embodiments of the present invention are notlimited thereto. For example, the base region 10 and the secondconductive region 30 may be of a p-type, and the first conductive region20 may be of an n-type.

The first conductive region 20 of the first conductive type, which isopposite to the second conductive type of the base region 10, may beformed at the front surface of the semiconductor substrate 110. Thefirst conductive region 20 may form a pn junction together with the baseregion 10 to constitute an emitter region for generating carriersthrough photoelectric conversion.

In this embodiment of the present invention, the first conductive region20 may be a doped region constituting a portion of the semiconductorsubstrate 110. In this case, the first conductive region 20 may beformed of a crystalline semiconductor having a first conductive dopant.For example, the first conductive region 20 may be formed of a singlecrystalline semiconductor (e.g. single crystalline silicon) or apolycrystalline semiconductor (e.g. polycrystalline silicon) having afirst conductive dopant. In particular, the first conductive region 20may be formed of a single crystalline semiconductor (e.g. a singlecrystalline semiconductor wafer, more specifically a single crystallinesilicon wafer) having a first conductive dopant. In an instance in whichthe first conductive region 20 constitutes a portion of thesemiconductor substrate 110 as described above, junction characteristicsbetween the first conductive region 20 and the base region 10 may beimproved.

However, the embodiments of the present invention are not limitedthereto. For example, the first conductive region 20 may be formed onthe semiconductor substrate 110 separately from the semiconductorsubstrate 110, which will hereinafter be described in more detail withreference to FIG. 9.

The first conductive type may be a p-type or an n-type. In an instancein which the first conductive region 20 is of a p-type, the firstconductive region 20 may be formed of a single crystalline semiconductoror a polycrystalline semiconductor doped with a group-III element, suchas boron (B), aluminum (Al), gallium (Ga), or Indium (In). On the otherhand, in an instance in which the first conductive region 20 is of ann-type, the first conductive region 20 may be formed of a singlecrystalline semiconductor or a polycrystalline semiconductor doped witha group-V element, such as phosphorus (P), arsenic (As), bismuth (Bi),or antimony (Sb). However, the embodiments of the present invention arenot limited thereto. Various materials may be used as the firstconductive dopant.

In the figure, the first conductive region 20 is shown as having ahomogeneous structure of a generally uniform doping concentration.However, the embodiments of the present invention are not limitedthereto. In another embodiment of the present invention, the firstconductive region 20 may have a selective structure, which willhereinafter be described in detail with reference to FIG. 8.

The second conductive region 30 of the second conductive type, which isthe same as the second conductive type of the base region 10, having ahigher doping concentration of a second conductive dopant than the baseregion 10, may be formed at the back surface of the semiconductorsubstrate 110. The second conductive region 30 may form a back surfacefield to constitute a back surface field region for preventing orreducing loss of the carriers due to recombination at the surface of thesemiconductor substrate 110 (more exactly, the back surface of thesemiconductor substrate 110).

In this embodiment of the present invention, the second conductiveregion 30 may be a doped region constituting a portion of thesemiconductor substrate 110. In this case, the second conductive region30 may be formed of a crystalline semiconductor having a secondconductive dopant. For example, the second conductive region 30 may beformed of a single crystalline semiconductor (e.g. single crystallinesilicon) or a polycrystalline semiconductor (e.g. polycrystallinesilicon) having a second conductive dopant. In particular, the secondconductive region 30 may be formed of a single crystalline semiconductor(e.g. a single crystalline semiconductor wafer, more specifically asingle crystalline silicon wafer) having a second conductive dopant. Inan instance in which the second conductive region 30 constitutes aportion of the semiconductor substrate 110 as described above, junctioncharacteristics between the second conductive region 30 and the baseregion 10 may be improved.

However, the embodiments of the present invention are not limitedthereto. For example, the second conductive region 30 may be formed onthe semiconductor substrate 110 separately from the semiconductorsubstrate 110, which will hereinafter be described in more detail withreference to FIG. 9.

The second conductive type may be an n-type or a p-type. In an instancein which the second conductive region 30 is of an n-type, the secondconductive region 30 may be formed of a single crystalline semiconductoror a polycrystalline semiconductor doped with a group-V element, such asphosphorus (P), arsenic (As), bismuth (Bi), or antimony (Sb). On theother hand, in an instance in which the second conductive region 30 isof a p-type, the second conductive region 30 may be formed of a singlecrystalline semiconductor or a polycrystalline semiconductor doped witha group-III element, such as boron (B), aluminum (Al), gallium (Ga), orIndium (In). However, the embodiments of the present invention are notlimited thereto. Various materials may be used as the second conductivedopant. The second conductive dopant of the second conductive region 30may be formed of a material identical to that of the second conductivedopant of the base region 10 or a material different from that of thesecond conductive dopant of the base region 10.

In this embodiment of the present invention, the second conductiveregion 30 is shown as having a homogeneous structure of a generallyuniform doping concentration. However, the embodiments of the presentinvention are not limited thereto. In another embodiment of the presentinvention, the second conductive region 30 may have a selectivestructure or a local structure, which will hereinafter be described indetail with reference to FIG. 8.

In this embodiment of the present invention, the first and secondconductive regions 20 and 30 formed at the semiconductor substrate 110are doped with the first and second conductive dopants, and the baseregion 10 is doped with the second conductive dopant. As a result, thedopants are distributed throughout the semiconductor substrate 110. Atthis time, any specific dopant may be combined with a different materialor element in the semiconductor substrate 110 to lower thecharacteristics of the solar cell 100. For example, in an instance inwhich the semiconductor substrate 110 has boron (B) as a dopant, boron(B) may react with oxygen (O) to form a B-O combination. Such a B-Ocombination may greatly reduce lifetime of the carriers, therebylowering the characteristics of the solar cell 100. Particularly, in aninstance in which boron (B) is used as the second conductive agentincluded in the base region 10, and therefore the base region 10 is of ap-type, a large amount of the B-O combination may be distributed overthe large area of the semiconductor substrate 110, thereby greatlylowering the characteristics of the solar cell 100.

In this embodiment of the present invention, therefore, apost-processing operation (ST50) (see FIG. 3) may be carried out suchthat any combination (e.g. the above-mentioned B-O combination) whichmay lower the characteristics of the solar cell 100 is not generated toprevent or reduce lowering or deterioration of the characteristics ofthe solar cell 100, which will hereinafter be described in more detailwhen describing a method of manufacturing the solar cell 100.

The semiconductor substrate 110 may have a thickness T1 of 200 μm orless. If the thickness T1 of the semiconductor substrate 110 is greaterthan 200 μm, it may be difficult for effects obtained by carrying outthe post-processing operation (ST50) to be exhibited throughout thesemiconductor substrate 110. For example, the semiconductor substrate110 may have a thickness T1 of 100 μm to 200 μm. If the thickness T1 ofthe semiconductor substrate 110 is less than 100 μm, the efficiency ofthe solar cell 100 may be decreased and the mechanical characteristicsof the solar cell 100 may not be sufficient since the thickness T1 ofthe semiconductor substrate 110 is insufficient to perform photoelectricconversion. However, the embodiments of the present invention are notlimited thereto. The thickness T1 of the semiconductor substrate 110 maybe variously changed.

The first passivation film 22 and the anti-reflection film 24 aresequentially formed on the front surface of the semiconductor substrate110, more exactly on the first conductive region 20 formed on thesemiconductor substrate 110, and the first electrode 42 is formed at thefirst conductive region 20 in contact through the first passivation film22 and the anti-reflection film 24 (i.e. via an opening 102 formedthrough the first passivation film 22 and the anti-reflection film 24).

The first passivation film 22 and the anti-reflection film 24 may besubstantially formed throughout the front surface of the semiconductorsubstrate 110 excluding the opening 102 corresponding to the firstelectrode 42.

The first passivation film 22 is formed at the first conductive region20 in contact to passivate defects existing on the surface of the firstconductive region 20 or in a bulk of the first conductive region 20. Thepassivation of defects may remove a recombination site of minoritycarriers, which may increase an open-circuit voltage Voc of the solarcell 100. The anti-reflection film 24 reduces the reflectance of lightincident upon the front surface of the semiconductor substrate 110.Through reduction in the reflectance of light incident upon the frontsurface of the semiconductor substrate 110, the quantity of lightreaching the pn junction formed by the base region 10 and the firstconductive region 20 may be increased with the result that ashort-circuit current Isc of the solar cell 100 may be increased. Asdescribed above, the first passivation film 22 and the anti-reflectionfilm 24 may increase the open-circuit voltage and the short-circuitcurrent of the solar cell 100, thereby improving the efficiency of thesolar cell 100.

The first passivation film 22 may be formed of various materials. Forexample, the first passivation film 22 may be formed of a dielectricmaterial including hydrogen. In an instance in which the firstpassivation film 22 includes hydrogen as described above, the firstpassivation film 22 may function to passivate the surface of thesemiconductor substrate 110 and, in addition, function as a hydrogensource for supplying hydrogen to the surface of the semiconductorsubstrate 110 or into a bulk of the semiconductor substrate 110 at thepost-processing operation (ST50).

For example, the first passivation film 22 may include 10²⁰ to 10²²ea/cm³ of hydrogen. The hydrogen content of the first passivation film22 is limited to a range in which the first passivation film 22 caneffectively function as the hydrogen source when the first passivationfilm 22 passivates the surface of the semiconductor substrate 110 and atthe post-processing operation (ST50). However, the embodiments of thepresent invention are not limited thereto. The hydrogen content of thefirst passivation film 22 may be variously changed.

For example, the first passivation film 22 may include a silicon nitride(SiNx:H) including hydrogen, a silicon oxide nitride (SiOxNy:H)including hydrogen, a silicon carbide (SiCx:H) including hydrogen, or asilicon oxide (SiOx:H) including hydrogen. However, the embodiments ofthe present invention are not limited thereto. The first passivationfilm 22 may include various other materials.

The first passivation film 22 may have a thickness of 50 nm to 200 nm.If the thickness of the first passivation film 22 is less than 50 nm,the passivation effect may not be sufficient, and the hydrogen diffusioneffect at the post-processing operation (ST50) may not be sufficient. Onthe other hand, if the thickness of the first passivation film 22 isgreater than 200 nm, the process time may be increased while the effectsare not greatly improved, and the thickness of the solar cell 100 may beincreased. However, the embodiments of the present invention are notlimited thereto. The thickness of the first passivation film 22 may bevariously changed.

The anti-reflection film 24 may be formed of various materials. Forexample, the anti-reflection film 24 may have a single film structure ora multi-layer film structure formed of at least one selected from agroup consisting of a silicon nitride, a silicon nitride includinghydrogen, a silicon oxide, a silicon oxide nitride, an aluminum oxide,MgF₂, ZnS, TiO₂, and CeO₂. For example, the anti-reflection film 24 mayinclude a silicon nitride.

In this embodiment of the present invention, the anti-reflection film 24formed at the semiconductor substrate 110 in contact includes hydrogensuch that the anti-reflection film 24 can effectively function topassivate the surface of the semiconductor substrate 110 and function asthe hydrogen source. However, the embodiments of the present inventionare not limited thereto. For example, only the anti-reflection film 24may include hydrogen, or both the anti-reflection film 24 and the firstpassivation film 22 may include hydrogen. In an instance in which theanti-reflection film 24 includes hydrogen, the material, hydrogencontent, thickness, etc. of the anti-reflection film 24 may be equal toor similar to those of the first passivation film 22.

Furthermore, in this embodiment of the present invention, the firstpassivation film 22, which is a dielectric film disposed at the frontsurface of the semiconductor substrate 110, includes hydrogen such thatthe first passivation film 22 can supply the hydrogen at thepost-processing operation (ST50). This is because a short-wavelengthlight is easily incident upon the front surface of the semiconductorsubstrate 110 with the result that undesired combination (e.g. theabove-mentioned B-O combination) may be highly generated, whereasgeneration of undesired combination is advantageously prevented orreduced when hydrogen is supplied to the front surface of thesemiconductor substrate 110. However, the embodiments of the presentinvention are not limited thereto. For example, a dielectric film formedon the front surface and/or the back surface of the semiconductorsubstrate 110 may include hydrogen such that the dielectric film cansupply the hydrogen at the post-processing operation (ST50).

In addition, in the above-described embodiment of the present invention,both the first passivation film 22 and the anti-reflection film 24 areincluded. However, the embodiments of the present invention are notlimited thereto. For example, any one selected from between the firstpassivation film 22 and the anti-reflection film 24 may perform both areflection preventing function and a passivation function in a state inwhich the other selected from between the first passivation film 22 andthe anti-reflection film 24 is not provided. In another example, variousfilms may be formed on the front surface of the semiconductor substrate110 in addition to the first passivation film 22 and the anti-reflectionfilm 24. Various other modifications are also possible.

The first electrode 42 is electrically connected to the first conductiveregion 20 through the first passivation film 22 and the anti-reflectionfilm 24 (i.e. via the opening 102 formed through the first passivationfilm 22 and the anti-reflection film 24). The first electrode 42 may beformed of various materials such that the first electrode 42 can havevarious shapes. The shape of the first electrode 42 will hereinafter bedescribed with reference to FIG. 2.

The second electrode 44 is formed on the back surface of thesemiconductor substrate 110, more exactly on the second conductiveregion 30 formed on the semiconductor substrate 110. In this embodimentof the present invention, the second electrode 44 is formed throughoutthe back surface of the semiconductor substrate 110 such that light canbe reflected by the back surface of the semiconductor substrate 110. Inthis case, light reaching the back surface of the semiconductorsubstrate 110 is reflected to the interior of the semiconductorsubstrate 110, thereby improving the efficiency in use of the light. Atthis time, the second electrode 44 may be formed at the back surface ofthe semiconductor substrate 110 or the second conductive region 30 incontact.

In this embodiment of the present invention, materials included in thesecond electrode 44 may be diffused into the semiconductor substrate 110to form the second conductive region 30 at the operation of firing thesecond electrode 44. As a result, an additional doping process forforming the second conductive region 30 may be omitted, therebysimplifying the manufacturing process of the solar cell 100. Inaddition, damage to the semiconductor substrate 110 or defects of thesemiconductor substrate 110, which may occur at a process of forming thesecond conductive region 30 through doping, may be prevented or reduced.

Hereinafter, the planar shape of the first electrode 42 will bedescribed in detail with reference to FIG. 2.

Referring to FIG. 2, the first electrode 42 may include a plurality offinger electrodes 42 a arranged at a uniform pitch such that the fingerelectrodes 42 a are spaced apart from each other. In the figure, thefinger electrodes 42 a are illustrated as being parallel to each otherand, in addition, parallel to the edge of the semiconductor substrate110. However, the embodiments of the present invention are not limitedthereto. The first electrode 42 may further include at least one bus barelectrode 42 b formed in a direction intersecting the finger electrodes42 a for interconnecting the finger electrodes 42 a. Only one bus barelectrode 42 b may be provided, or a plurality of bus bar electrodes 42b arranged at a larger pitch than the finger electrodes 42 a may beprovided as shown in FIG. 2. In this case, the width of each of the busbar electrodes 42 b may be greater than that of each of the fingerelectrodes 42 a. However, the embodiments of the present invention arenot limited thereto. For example, the width of each of the bus barelectrodes 42 b may be equal to or less than that of each of the fingerelectrodes 42 a.

When viewed in section, the finger electrodes 42 a and the bus barelectrodes 42 b of the first electrode 42 may be formed through thefirst passivation film 22 and the anti-reflection film 24. That is, theopening 102 may be formed through the first passivation film 22 and theanti-reflection film 24 such that the opening 102 corresponds to thefinger electrodes 42 a and the bus bar electrodes 42 b. In anotherexample, the finger electrodes 42 a of the first electrode 42 may beformed through the first passivation film 22 and the anti-reflectionfilm 24, and the bus bar electrodes 42 b of the first electrode 42 maybe formed on the first passivation film 22 and the anti-reflection film24. In this case, the opening 102 may be formed through the firstpassivation film 22 and the anti-reflection film 24 such that theopening 102 corresponds to the finger electrodes 42 a but not the busbar electrodes 42 b.

The solar cell 100 may be processed so as to prevent or reducegeneration of any combination which may lower the characteristics of thesolar cell 100 at the post-processing operation (ST50) as previouslydescribed, which will hereinafter be described in more detail whendescribing a manufacturing method of the solar cell 100.

FIG. 3 is a flowchart showing a manufacturing method of a solar cellaccording to an embodiment of the present invention, and FIGS. 4A to 4Gare sectional views showing the manufacturing method of the solar cellshown in FIG. 3. A detailed description will not be given of parts ofthe solar cell shown in FIGS. 3 and 4A to 4G identical to or similar tothose of the solar cell 100 described with reference to FIGS. 1 and 2.Hereinafter, only parts of the solar cell shown in FIGS. 3 and 4A to 4Gdifferent from those of the solar cell 100 described with reference toFIGS. 1 and 2 will be described in more detail.

Referring to FIG. 3, the manufacturing method of the solar cell 100according to the embodiment of the present invention includes asemiconductor substrate preparing operation (ST10), a conductive regionforming operation (ST20), a dielectric film forming operation (ST30), anelectrode forming operation (ST40), and a post-processing operation(ST50). The electrode forming operation (ST40) may include an operationof forming first and second electrode layers (ST42) and a firingoperation (ST44). The post-processing operation (ST50) may include ahydrogen diffusion process (ST52), a preliminary heat treatment process(ST54), and a main processing process (ST56). The firing operation(ST44) and the hydrogen diffusion process (ST52) may be simultaneouslycarried out. The manufacturing method of the solar cell 100 according tothe embodiment of the present invention will be described in detail withreference to FIGS. 4A to 4G.

First, as shown in FIG. 4A, a semiconductor substrate 110 including abase region 10 having a second conductive dopant is prepared at thesemiconductor substrate preparing operation (ST10). For example, in thisembodiment of the present invention, the semiconductor substrate 110 maybe formed of a silicon substrate (e.g. a silicon wafer) having a p-typedopant (specifically boron (B)). However, the embodiments of the presentinvention are not limited thereto. For example, the base region 10 mayhave a p-type dopant other than boron or an n-type dopant.

At this time, the front surface and/or the back surface of thesemiconductor substrate 110 may be textured such that front surfaceand/or the back surface of the semiconductor substrate 110 has a ruggedshape (irregular or textured shape). The surface of the semiconductorsubstrate 110 may be textured using wet texturing or dry texturing. Inthe wet texturing, the semiconductor substrate 110 is soaked in atexturing solution. The wet texturing has an advantage in that theprocess time is short. In the dry texturing, on the other hand, thesurface of the semiconductor substrate 110 is cut using a diamond grillor a laser. In the dry texturing, a rugged shape is uniformly formed.However, the process time is long, and the semiconductor substrate 110may be damaged. Alternatively, the semiconductor substrate 110 may betextured using reactive ion etching (RIE), etc. As described above, thesemiconductor substrate 110 may be textured using various methods.

For example, the front surface of the semiconductor substrate 110 may betextured such that the front surface of the semiconductor substrate 110has a rugged shape, and the back surface of the semiconductor substrate110 may be mirror-ground to have a lower surface roughness than thefront surface of the semiconductor substrate 110. However, theembodiments of the present invention are not limited thereto. Thesemiconductor substrate 110 may have various other structures.

Subsequently, as shown in FIG. 4B, a conductive region is formed at thesemiconductor substrate 110 at the conductive region forming operation(ST20). More specifically, in this embodiment of the present invention,a first conductive region 20 is formed at the front surface of thesemiconductor substrate 110 at the conductive region forming operation,and a second conductive region 30 (see FIG. 4E), which will bepositioned at the back surface of the semiconductor substrate 110, isformed at a subsequent operation of firing a second electrode 44.However, the embodiments of the present invention are not limitedthereto. For example, the first conductive region 20 and/or the secondconductive region 30 may be formed at the conductive region formingoperation. In this case, the second conductive region 30 may be formedusing a method identical to or similar to a method of forming the firstconductive region 20, which will hereinafter be described.

The first conductive region 20 may be formed by doping a dopant usingvarious methods, such as ion injection, thermal diffusion, and laserdoping. In another example, an additional layer having a firstconductive dopant may be formed on the semiconductor substrate 110 toform the first conductive region 20.

Subsequently, as shown in FIG. 4C, a dielectric film is formed on thefront surface of the semiconductor substrate 110 or on the firstconductive region 20 at the dielectric film forming operation (ST30).

More specifically, a first passivation film 22 and an anti-reflectionfilm 24 are formed on the first conductive region 20. In this embodimentof the present invention, no dielectric film is positioned at the backsurface of the semiconductor substrate 110. Alternatively, anotherdielectric film (e.g. a second passivation film) may be positioned atthe back surface of the semiconductor substrate 110. The dielectric filmmay also be formed at the back surface of the semiconductor substrate110 at this operation. In this case, the dielectric film may also beformed on the back surface of the semiconductor substrate 110 using amethod identical to or similar to a method of forming the firstpassivation film 22 and the anti-reflection film 24, which willhereinafter be described.

The first passivation film 22 and/or the anti-reflection film 24 may beformed using various methods, such as vacuum deposition, chemical vapordeposition, spin coating, screen printing, and spray coating.

In this embodiment of the present invention, the first passivation film22 may be formed of a dielectric material including hydrogen. As aresult, the first passivation film 22 may function to passivate thesurface of the semiconductor substrate 110 using hydrogen and, inaddition, function as a hydrogen source for supplying hydrogen to thesemiconductor substrate 110 at the post-processing operation (ST50).

Subsequently, as shown in FIGS. 4D and 4E, first and second electrodes42 and 44 are formed at the electrode forming step (ST40), which willhereinafter be described in more detail.

First, as shown in FIG. 4D, a paste for forming first and secondelectrodes is applied onto the dielectric films, such as the firstpassivation film 22 and the anti-reflection film 24, or thesemiconductor substrate 110 by printing (e.g. screen printing) to formfirst and second electrode layers 420 and 440 at the operation offorming the first and second electrode layers (ST42). The first andsecond electrode layers 420 and 440 may be formed using various othermethods or processes.

Subsequently, as shown in FIG. 4E, the first and second electrode layers420 and 440 are fired to form first and second electrodes 42 and 44 atthe firing operation (ST44).

During firing, an opening 102 is formed through the dielectric films,such as the first passivation film 22 and the anti-reflection film 24,by firing through or laser firing contact with the result that the firstelectrode layer 420 is connected to (e.g. contacts) the first conductiveregion 20. In an instance in which the firing through or the laserfiring contact is used as described above, the opening 102 is formedduring firing. As a result, it is not necessary to carry out anadditional process of forming the opening 102.

In addition, a material (e.g. aluminum) constituting the secondelectrode 44 may be diffused to the back surface of the semiconductorsubstrate 110 to form the second conductive region 30 at thesemiconductor substrate 110. However, the embodiments of the presentinvention are not limited thereto. For example, the second conductiveregion 30 may be formed at the conductive region forming operation(ST20) as previously described.

For example, at the firing operation (ST44), temperature (specifically,peak temperature) may be 700 to 800° C., and process time may be 5 to 20seconds. These conditions are limited to a range in which process timecan be minimized while firing is sufficiently achieved. However, theembodiments of the present invention are not limited thereto. Inaddition, the firing operation (ST44) may be carried out using heatgenerated from an ultraviolet lamp. However, the embodiments of thepresent invention are not limited thereto. Various other methods mayalso be used.

As described above, in this embodiment of the present invention, theelectrode forming operation (ST40) includes the firing operation (ST44).The firing operation (ST44) may be a part of the post-processingoperation (S50), which will be subsequently carried out. That is, thefiring operation (ST44) and a part of the post-processing operation(S50) may be simultaneously carried out, which will hereinafter bedescribed in more detail when describing the post-processing operation(S50).

However, the embodiments of the present invention are not limitedthereto. The electrode forming operation (ST40) may not include thefiring operation (ST44). For example, the opening 102 may be formedthrough the first passivation film 22 and the anti-reflection film 24,the opening 102 may be filled with a conductive material using variousmethods, such as plating and deposition, to form the first electrode 42,and the second electrode 44 may be formed using various methods, such asplating, deposition, and printing. In addition, the first electrode 42and the second electrode 44 may be formed using various other methods.

Subsequently, the post-processing operation (S50) is carried out topost-process the solar cell 100 including the semiconductor substrate110 by passivating the semiconductor substrate 110. More specifically,the post-processing operation (S50) is carried out to prevent loweringin characteristics of the solar cell 100 which may be caused due to aspecific combination generated at the surface of the semiconductorsubstrate 110 or in the bulk of the semiconductor substrate 110. Forexample, in an instance in which the semiconductor substrate 110includes boron, the B-O combination may be easily generated in thesemiconductor substrate 110 when light is supplied to the semiconductorsubstrate 110. Such a B-O combination may greatly reduce the lifetime ofthe carriers, thereby lowering the characteristics of the solar cell100. In this embodiment of the present invention, therefore, thepost-processing operation (S50) is carried out such that specificcombination (e.g. the B-O combination) which may lower thecharacteristics of the solar cell 100 is not generated in thesemiconductor substrate 110 as described above, thereby improving thecharacteristics of the solar cell 100.

In an instance in which the semiconductor substrate 110 is heat-treatedat a high temperature after the post-processing operation (S50), theeffects obtained by the post-processing operation (S50) may be loweredor disappear. For this reason, the post-processing operation (S50) maybe carried out in the second half of the manufacturing method of thesolar cell 100. Specifically, the post-processing operation (S50) may becarried out simultaneously with the firing operation (ST44) or after thefiring operation (ST44), which is carried out at a relatively hightemperature. For example, a part of the post-processing operation (S50)may be carried out simultaneously with the firing step (ST44), and therest of the post-processing operation (S50) may be carried out after thefiring operation (ST44). Alternatively, the entirety of thepost-processing operation (S50) may be carried out after the firingoperation (ST44). As a result, the effects obtained by thepost-processing operation (S50) may not be lowered or disappear. Thepost-processing operation (S50) will hereinafter be described in moredetail.

The post-processing operation (S50) includes the main processing process(ST56), which is capable of restraining generation of combinationlowering the characteristics of the solar cell 100 and generatingcombination (e.g. a B-H combination) which may not badly or adverselyaffect the characteristics of the solar cell 100 through heat treatmentof the semiconductor substrate together with the supply of light to thesemiconductor substrate. In addition, the post-processing operation(S50) may further include the hydrogen diffusion process (ST52) and/orthe preliminary heat treatment process (ST54), which are carried outbefore the main processing process (ST56), for improving the effects ofthe main processing process (ST56). In this embodiment of the presentinvention, the hydrogen diffusion process (ST52), the preliminary heattreatment process (ST54), and the main processing process (ST56) aresequentially carried out to maximize the effects of the post-processingoperation (S50). Hereinafter, the hydrogen diffusion process (ST52), thepreliminary heat treatment process (ST54), and the main processingprocess (ST56) will be described in detail.

First, hydrogen is diffused in the semiconductor substrate 110 at thehydrogen diffusion process (ST52). At the hydrogen diffusion process(ST52), the semiconductor substrate 110 is heat-treated at a hightemperature at which hydrogen is diffused deeply in the semiconductorsubstrate 110.

At this time, hydrogen may be supplied from various hydrogen sources tothe semiconductor substrate 110. For example, the semiconductorsubstrate 110 may be placed in a furnace under a hydrogen atmospheresuch that hydrogen in the hydrogen atmosphere can be supplied into thesemiconductor substrate 110. In this case, the hydrogen in the hydrogenatmosphere is a hydrogen source. Alternatively, in an instance in whichthe dielectric films (i.e. the first passivation film 22 and theanti-reflection film 24) formed on the semiconductor substrate 110include hydrogen, the hydrogen from the dielectric films may be suppliedinto the semiconductor substrate 110 by heat treatment. In this case,the hydrogen in the dielectric films is a hydrogen source.

In this embodiment of the present invention, the dielectric films,specifically the first passivation film 22 contacting the semiconductorsubstrate 110, include hydrogen, and the hydrogen is supplied into thesemiconductor substrate 110. In an instance in which the firstpassivation film 22 is used as a hydrogen source as described above, itis not necessary to provide a process or an apparatus for forming thehydrogen atmosphere. In addition, the first passivation film 22 mayfunction as a kind of capping film for further accelerating thediffusion of hydrogen in the semiconductor substrate 110.

The hydrogen diffusion process (ST52) may be carried out at atemperature (more exactly, a peak temperature) of 400 to 800° C. (morespecifically, 400 to 700° C.) for 5 seconds to 20 minutes (morespecifically, 1 to 20 minutes). If the temperature of the hydrogendiffusion process (ST52) is less than 400° C. or the process time isless than 5 seconds, hydrogen diffusion may not be sufficientlyachieved. On the other hand, if the temperature of the hydrogendiffusion process (ST52) is greater than 800° C. or the process time isgreater than 20 minutes, a process cost and time are increased, therebylowering productivity. In other words, hydrogen may be effectivelydiffused in the semiconductor substrate 110 within the above-definedtemperature and time ranges, thereby achieving high productivity. Inconsideration of the process cost and the productivity, the temperatureof the hydrogen diffusion process (ST52) may be 400 to 700° C. Inconsideration of the hydrogen diffusion, on the other hand, the processtime may be 1 to 20 minutes. However, the embodiments of the presentinvention are not limited thereto. The temperature and the process timeof the hydrogen diffusion process (ST52) may be variously changed.

At this time, various heat source units which are capable of uniformlymaintaining the temperature of the hydrogen diffusion process (ST52) maybe used. For example, an ultraviolet lamp or a resistance heating typeheater may be used as a heat source unit. However, the embodiments ofthe present invention are not limited thereto. Various other heat sourceunits may be used.

The temperature and the process time of the hydrogen diffusion process(ST52) may be equal to, similar to, or overlap with those of the firingoperation (ST44) of the electrode forming operation (ST40). In addition,heat source units used at the hydrogen diffusion process (ST52) and thefiring operation (ST44) may be identical to or similar to each other.Consequently, the hydrogen diffusion process (ST52) may be carried outsimultaneously with the firing operation (ST44). That is, as shown inFIG. 4E, hydrogen diffusion may be achieved at the firing operation(ST44) without additionally carrying out the hydrogen diffusion process(ST52). Since the hydrogen diffusion process (ST52) is not additionallycarried out, the process may be simplified, and process cost may bereduced. However, the embodiments of the present invention are notlimited thereto. For example, the hydrogen diffusion process (ST52) maybe carried out as a separate operation after the firing operation(ST44).

Subsequently, as shown in FIG. 4F, the preliminary heat treatmentprocess (ST54) may be carried out to heat-treat the semiconductorsubstrate 110 such that hydrogen diffused in the semiconductor substrate110 can react with a different material and element in the semiconductorsubstrate 110 to generate a combination including the hydrogen. Inparticular, the hydrogen may be combined with the dopant of thesemiconductor substrate 110. For example, in an instance in which thesemiconductor substrate 110 includes boron as a dopant, the B-Hcombination, in which hydrogen and boron are combined with each other,may be generated.

At the preliminary heat treatment process (ST54), only heat treatment iscarried out without additional supply of light to the semiconductorsubstrate with the result that the B-O combination is not generated butthe B-H combination is generated. As described above, no light issupplied at the preliminary heat treatment process (ST54). Even in aninstance in which natural light is supplied, the light has a lightintensity of about 100 mW/cm², which is lower than that of the mainprocessing process (ST56). However, the embodiments of the presentinvention are not limited thereto. The light intensity of thepreliminary heat treatment process (ST54) may be changed.

The temperature of the preliminary heat treatment process (ST54) may be100 to 300° C., which is lower than that of the hydrogen diffusionprocess (ST52). As previously described, the preliminary heat treatmentprocess (ST54) is carried out to generate the B-H combination. If thetemperature of the preliminary heat treatment process (ST54) is lessthan 100° C., no energy for the B-H combination is provided with theresult that the B-H combination may not be satisfactorily generated. Onthe other hand, if the temperature of the preliminary heat treatmentprocess (ST54) is greater than 300° C., hydrogen combination is superiorto the B-H combination. As a result, hydrogen combination may begenerated, and the B-H combination may be decomposed. In an instance inwhich the temperature of the preliminary heat treatment process (ST54)is 100 to 300° C., therefore, it is possible to generate a large amountof the B-H combination through the preliminary heat treatment process(ST54).

The process time of the preliminary heat treatment process (ST54) may be1 to 30 minutes. If the process time of the preliminary heat treatmentprocess (ST54) is less than 1 minute, it may be difficult tosufficiently generate the desired B-H combination. On the other hand, ifthe process time of the preliminary heat treatment process (ST54) isgreater than 30 minutes, the process time may be increased while theeffects obtained through preliminary heat treatment are not greatlyimproved, thereby lowering productivity. However, the embodiments of thepresent invention are not limited thereto. The process time of thepreliminary heat treatment process (ST54) may be changed.

In an instance in which the B-H combination is generated through thepreliminary heat treatment process (ST54) as described above, hydrogenexists near the surface of the semiconductor substrate 110 or in thesemiconductor substrate 110 in a state in which the hydrogen is combinedwith boron (B), which is the dopant of the semiconductor substrate 110.In particular, a large amount of the B-H combination exists near thesurface of the semiconductor substrate 110. As a result, the diffusiondistance and time of hydrogen into the semiconductor substrate 110 maybe reduced at the main processing process (ST56), which will besubsequently carried out.

Subsequently, as shown in FIG. 4G, the semiconductor substrate 110 isheat-treated at a temperature higher than a room temperature in a statein which light is supplied to the semiconductor substrate 110 at themain processing process (ST56). In an instance in which light issupplied to the semiconductor substrate 110 at the main processingprocess (ST56), hydrogen may not be in an H⁺ state, in which thehydrogen is stable, but may be in an H⁰ or H-state, in which thehydrogen is unstable, even during a short time by carrier injection fromthe light. Since the hydrogen in the H⁰ or H⁻ state is not stable, thestate of the hydrogen may be converted into the H⁺ state, in which thehydrogen is stable, after a predetermined time.

Since the diffusion speed of the hydrogen in the H⁰ or H⁻ stategenerated by the light is much greater than that of the hydrogen in theH⁺ state, the hydrogen may be rapidly diffused in the semiconductorsubstrate 110. Consequently, the hydrogen is uniformly distributed inthe semiconductor substrate 110 with the result that the hydrogenfunctions to remove defects in the semiconductor substrate 110 or toprevent or reduce generation of undesired combination in thesemiconductor substrate 110. For example, in an instance in which thehydrogen in the H⁰ or H⁻ state is diffused in the semiconductorsubstrate 110 and is then converted into the H⁺ state, in which thehydrogen is stable, the B-H combination is generated, thereby preventingor reducing generation of the B-O combination. That is, the B-Ocombination, which may generated at the beginning of the main processingprocess (ST56) due to light emitted to the semiconductor substrate 110,may be decomposed to generate B-H combination. After that, the B-Hcombination is generally predominant in the semiconductor substrate 110with the result that the B-O combination is not generated. As describedabove, the B-H combination, which is distributed at the surface of thesemiconductor substrate 110, may be uniformly distributed in thesemiconductor substrate 110, thereby preventing or reducing generationof the undesired B-O combination in the semiconductor substrate 110.

In this embodiment of the present invention, it is necessary to providethe temperature, the light intensity, and the time based on apredetermined relationship thereamong so as to convert the hydrogen inthe H⁺ state into the hydrogen in the H⁰ or H⁻ state, and to concretelydefine the relationship so as to maximize the effects of the mainprocessing process (ST56). That is, if a predetermined light intensityand/or process time is not provided although light is supplied to thesemiconductor substrate at a uniform temperature, hydrogen exists in theH⁺ state, in which the hydrogen is stable. Only when the predeterminedlight intensity and/or process time is provided, the state of thehydrogen may be converted into the H⁰ or H⁻ state.

At this time, the main processing process (ST56) may be carried out tohave a time-temperature graph as shown in FIG. 5. FIG. 5 is a graphshowing a relationship between time and temperature of the mainprocessing process of the post-processing operation of the manufacturingmethod of the solar cell according to the embodiment of the presentinvention.

That is, as shown in FIG. 5, the main processing process (ST56) mayinclude a main period (ST562) having a temperature (more specifically, apeak temperature) for hydrogen conversion. The main processing process(ST56) may further include a temperature rising period (ST561) forincreasing the temperature from the room temperature to the temperatureof the main period, the temperature rising period (ST561) being carriedout before the main period (ST562), and a cooling period (ST563) fordecreasing the temperature to the room temperature, the cooling period(ST563) being carried out after the main period (ST562). During the mainprocessing process (ST56), therefore, the occurrence of problems causeddue to abrupt change of temperature may be prevented, and a desiredreaction may be stably achieved. In this embodiment of the presentinvention, the temperature of the main processing process (ST56) meansthat of the main period (ST562), in which hydrogen conversion isactually achieved. The light intensity of the main processing process(ST56) may mean that of the main period (ST562), and the process time ofthe main processing process (ST56) may mean that of the main period(ST562), in which hydrogen conversion is actually achieved.

It is necessary that the temperature of the main processing process(ST56) be sufficient to convert hydrogen in an H⁺ state into hydrogen inan H⁰ or H⁻ state and to decompose the B-O combination which may begenerated due to the supply of light. For example, the temperature ofthe main processing process (ST56) may be 100 to 800° C. If thetemperature of the main processing process (ST56) is less than 100° C.,thermal energy is less than energy necessary to decompose the B-Ocombination with the result that the B-O combination generated due tothe supply of light may survive. On the other hand, if the temperatureof the main processing process (ST56) is greater than 800° C., a processcost may be increased due to the high temperature. However, theembodiments of the present invention are not limited thereto.

First, a relationship between temperature and light intensity of themain processing process (ST56) for converting hydrogen in an H⁺ stateinto hydrogen in an H⁰ or H⁻ state will be described before arelationship between light intensity and time of the main processingprocess (ST56) will be described.

FIG. 6 is a graph showing a state of hydrogen based on a relationshipbetween temperature and light intensity at the post-processing operationof the manufacturing method of the solar cell according to theembodiment of the present invention.

A relationship between temperature and light intensity was analyzedbased on the fact that the minimum value I_(min) of the light intensitynecessary for hydrogen conversion varies according to temperature T ofthe main processing process (ST56). The results were obtained as shownin FIG. 6. It can be seen from FIG. 6 that the minimum value I_(min) ofthe light intensity increases as the temperature T of the mainprocessing process (ST56) increases. In this embodiment of the presentinvention, therefore, the minimum value I_(min) of the light intensityper temperature T is represented by Equation 1.

I _(min)=1750−31.8·T+(0.16)·T ²  <Equation 1>

-   -   where the unit of T is ° C., and the unit of I_(min) is mW/cm².

Only in an instance in which light intensity I of light suppliedsimultaneously with heat treatment is equal to or greater than theminimum value I_(min) of the light intensity on the assumption that thetemperature T of the main processing process (ST56) has a uniform value,therefore, the state of the hydrogen may be converted into the H⁰ or H⁻state. For reference, in an instance in which the temperature T is 100to 800° C., the minimum value I_(min) of the light intensity may be1.7×10² mW/cm² to 7.871×10⁴ mW/cm².

Consequently, the light intensity I of the light to be supplied based onthe temperature T of the main processing process (ST56) may satisfy theconditions of Equation 2.

1750−31.8·T+(0.16)·T ² ≤I  <Equation 2>

-   -   where the unit of T is ° C., and the unit of I is mW/cm².

In an instance in which the light intensity I of the light satisfyingEquation 2 is provided at a specific temperature T of the mainprocessing process (ST56), therefore, hydrogen in the H+ state may beconverted into hydrogen in the H⁰ or H⁻ state. At this time, it may bedifficult to acquire a desired value of the light intensity I of thelight if the light intensity I is excessively high. The light intensityI may have a value of 10⁵ mW/cm² within a range of the temperature T ofthe main processing process (ST56). Consequently, the light intensity Ito be provided based on the temperature T of the main processing process(ST56) may satisfy the conditions of Equation 3.

1750−31.8·T+(0.16)·T ² ≤I≤10⁵  <Equation 3>

-   -   where the unit of T is ° C., and the unit of I is mW/cm².

The above-described range of the temperature T and the ranges of thetemperature T and the light intensity I satisfying Equation 3approximately correspond to a region denoted by A in FIG. 6.

A relationship between light intensity and process time was analyzedbased on the fact that the minimum value P_(min) of the process timenecessary for hydrogen conversion (the minimum process time necessary toconvert hydrogen in the H+ state into hydrogen in the H⁰ state) variesaccording to the light intensity I of the main processing process(ST56). The results were obtained as shown in FIG. 7. FIG. 7 is a graphshowing a state of hydrogen based on a relationship between lightintensity and process time at the post-processing operation of themanufacturing method of the solar cell according to the embodiment ofthe present invention.

As shown in FIG. 7, the minimum value P_(min) of the process timedecreases as the light intensity I increases. That is, in an instance inwhich the light intensity I is high, a relatively short process time isneeded. On the other hand, in an instance in which the light intensity Iis low, a relatively long process time is needed. In this embodiment ofthe present invention, the minimum value P_(min) of the process timebased on the light intensity I approximately corresponds to Equations 4to 7. In an instance in which the light intensity I is 5×10₄ mW/cm² ormore as represented by Equation 7, the minimum process time is greatlydecreased with the result that it is difficult to perform arithmeticcalculation. In addition, it is difficult to carry out the processwithin the decreased process time. For this reason, it is assumed thatthe minimum value P_(min) of the process time is uniform for theabove-mentioned light intensity I.

1.7×10² ≤I<10³, and P _(min)=13000−(31.7)·1+(0.02)·(I)²  <Equation 4>

10³ ≤I<10⁴, and P _(min)=1030−(0.25)·I+(1.5×10⁻⁵)·(I)²  <Equation 5>

10⁴ ≤I≤5×10⁴, and P _(min)=35.5−(0.0012)·I+(10⁻⁸)·(I)²  <Equation 6>

5×10⁴ ≤I≤10⁵, and P _(min)=0.5  <Equation 7>

-   -   where the unit of I is mW/cm², and the unit of P_(min) is sec.

In an instance in which the process time P of the main processingprocess (ST56) is equal to or greater than the minimum value P_(min) ofthe process time when the light intensity I of the main processingprocess (ST56) has a uniform value, therefore, the state of the hydrogenmay be effectively converted into the H⁰ or H⁻ state. Consequently, theprocess time P of the main processing process (ST56) based on the lightintensity I may satisfy any one of Equations 8 to 11.

1.7×10² ≤I<10³, and 13000−(31.7)·I+(0.02)·(I)² ≤P  <Equation 8>

10³ ≤I<10⁴, and 1030−(0.25)·I+(1.5×10⁵)·(I)² ≤P  <Equation 9>

10⁴ ≤I≤5×10⁴, and 35.5−(0.0012)·I+(10⁻⁸)·(I)² ≤P  <Equation 10>

5×10⁴ ≤I≤10⁵, and 0.5≤P  <Equation 11>

-   -   where the unit of I_(min) is mW/cm², and the unit of P is sec.

In an instance in which the process is carried out with the lightintensity I of the main processing process (ST56) during the processtime P satisfying Equations 8 to 11, therefore, it is possible toconvert the hydrogen in the H⁺ state into the hydrogen in the H⁰ or H⁻state. At this time, productivity may be lowered if the process time Pis excessively long. For this reason, the process time P of the mainprocessing process (ST56) may have a value of 10,000 sec or less.Consequently, the process time P of the main processing process (ST56)based on the light intensity I may satisfy any one of Equations 12 to15.

1.7×10² ≤I<10³, and 13000−(31.7)·I+(0.02)·(I)² ≤P≤10000  <Equation 12>

10³ ≤I<10⁴, and 1030−(0.25)·I+(1.5×10⁵)·(I)² ≤P≤10000  <Equation 13>

10⁴ ≤I<5×10⁴, and 35.5−(0.0012)·I+(10⁻⁸)·(I)² ≤P≤10000  <Equation 14>

5×10⁴ ≤I≤10⁵, and 0.5≤P≤10000  <Equation 15>

The ranges of the light intensity I and the process time P satisfyingEquations 12 to 15 approximately correspond to a region denoted by B inFIG. 7.

As described above, in this embodiment of the present invention, theranges of the temperature T and the light intensity I of the mainprocessing process (ST56) are defined to achieve hydrogen conversion. Inaddition, the range of the process time P is also defined to effectivelyachieve hydrogen conversion. Consequently, it is possible to effectivelyprevent lowering in characteristics of the semiconductor substrate 110which may be caused in the semiconductor substrate 110 when light isemitted to the semiconductor substrate 110.

As described above, in this embodiment of the present invention, thepost-processing operation (ST50) includes the main processing process(ST56) which is carried out at predetermined ranges of the temperature Tand the light intensity I, thereby preventing undesired combination(e.g. the B-O combination), which may lower the characteristics of thesolar cell 100, from being generated in the semiconductor substrate 110and, instead, generating combination including hydrogen (e.g. the B-Hcombination) in the semiconductor substrate 110. Consequently, it ispossible to prevent lowering in characteristics of the solar cell 100due to undesired combination. At this time, the process time P of themain processing process (ST56) may be defined to be within apredetermined range to more effectively prevent generation of undesiredcombination.

In addition, the hydrogen diffusion process (ST52) for diffusinghydrogen and/or the preliminary heat treatment process (ST54) forgenerating combination including hydrogen (e.g. the B-H combination) maybe further carried out before the main processing process (ST56) tofurther improve the effects of the post-processing operation (ST50).

In the above description, the base region 10 of the semiconductorsubstrate 110 includes boron (B). Alternatively, the first conductiveregion 20 may include boron (B). Even in an instance in which thesemiconductor substrate 110 does not include boron (B), combinationincluding hydrogen (e.g. the B-H combination) may be generated in thesemiconductor substrate 110, thereby improving the characteristics ofthe solar cell 100.

In addition, the manufacturing method of the solar cell 100 according tothe embodiment of the present invention may be applied to manufacture ofa solar cell 100 including a semiconductor substrate 110 having acrystalline structure. Such a solar cell 100 will hereinafter bedescribed in detail with reference to FIGS. 8 and 9. Parts identical toor similar to those of the solar cell according to the previousembodiment of the present invention may be equally applied to thefollowing embodiments of the present invention, and therefore a detaileddescription thereof will be omitted.

FIG. 8 is a sectional view showing another example of the solar cellmanufactured using the manufacturing method of the solar cell accordingto the embodiment of the present invention.

Referring to FIG. 8, the solar cell according to this embodiment isconfigured such that a second passivation film 32 is formed on a backsurface of a semiconductor substrate 110, and a second electrode 44 isconnected to a second conductive region 30 through the secondpassivation film 32 (i.e. via an opening 104).

The second passivation film 32 may be substantially formed throughoutthe back surface of the semiconductor substrate 110 excluding theopening 104 corresponding to the second electrode 44. The secondpassivation film 32 is formed at the second conductive region 30 incontact to passivate defects existing on the surface of the secondconductive region 30 or in a bulk of the second conductive region 30.The passivation of defects may remove a recombination site of minoritycarriers, which may increase an open-circuit voltage Voc of the solarcell 100.

The second passivation film 32 may be formed of various materials. Forexample, the second passivation film 32 may be formed of a dielectricmaterial including hydrogen. In an instance in which the secondpassivation film 32 includes hydrogen as described above, the secondpassivation film 32 may function to passivate the surface of thesemiconductor substrate 110 and, in addition, function as a hydrogensource for supplying hydrogen to the surface of the semiconductorsubstrate 110 or into a bulk of the semiconductor substrate 110 at apost-processing operation (ST50) (see FIG. 3).

For example, the second passivation film 32 may include 10²⁰ to 10²²ea/cm³ of hydrogen. The hydrogen content of the second passivation film32 is limited to a range in which the second passivation film 32 caneffectively function as the hydrogen source when the second passivationfilm 32 passivates the surface of the semiconductor substrate 110 and atthe post-processing operation (ST50). However, the embodiments of thepresent invention are not limited thereto. The hydrogen content of thesecond passivation film 32 may be variously changed.

For example, the second passivation film 32 may include a siliconnitride (SiNx:H) including hydrogen, a silicon oxide nitride (SiOxNy:H)including hydrogen, a silicon carbide (SiCx:H) including hydrogen, or asilicon oxide (SiOx:H) including hydrogen. However, the embodiments ofthe present invention are not limited thereto. The second passivationfilm 32 may include various other materials.

As described above, in this embodiment of the present invention, boththe first passivation film 22 formed at the front surface of thesemiconductor substrate 110 and the second passivation film 32 formed atthe back surface of the semiconductor substrate 110 function as ahydrogen source at the post-processing operation (ST50), therebydoubling the effects of the post-processing operation (ST50).

However, the embodiments of the present invention are not limitedthereto. The second passivation film 32 may include various materials.Alternatively, only the second passivation film 32 may include hydrogen,and the first passivation film 22 may not include hydrogen. In addition,various films may be formed on the back surface of the semiconductorsubstrate 110 in addition to the second passivation film 32. Variousother modifications are also possible.

The second electrode 44 is electrically connected to the secondconductive region 30 via the opening 104 formed through the secondpassivation film 32. The second electrode 44 may be formed of variousmaterials such that the second electrode 44 can have various shapes.

For example, the second electrode 44 may have a planar shape identicalto or similar to that of the first electrode 42 previously describedwith reference to FIGS. 1 and 2. Consequently, the semiconductorsubstrate 110 has a bi-facial structure in which light is incident uponboth the front surface and the back surface of the semiconductorsubstrate 110. As a result, the quantity of light used for photoelectricconversion is increased, thereby improving the efficiency of the solarcell 100. The width and pitch of finger electrodes and bus barelectrodes of the second electrode 44 may be equal to or different fromthose of the finger electrodes 42 a and bus bar electrodes 42 b of thefirst electrode 42.

In another example, the second electrode 44 may be formed throughout thesecond passivation film 32 and may be connected to the back surface ofthe semiconductor substrate 110 or the second conductive region 30 inpoint contact via the opening 104. In this case, the back surface of thesemiconductor substrate 10 is not textured. That is, no rugged shape isformed at the back surface of the semiconductor substrate 10.Consequently, light may be effectively reflected by the second electrode44 formed throughout the second passivation film 32. Various othermodifications are also possible.

In this embodiment of the present invention, not only the firstconductive region 20 has a selective structure but also the secondconductive region 30 has a selective structure.

That is, the first conductive region 20 may include a first part 20 aformed adjacent to (e.g. in contact with) the first electrode 42 and asecond part 20 b formed at a region where the first electrode 42 is notpositioned. The first part 20 a has a relatively high dopantconcentration and a relatively large junction depth. Consequently, thefirst part 20 a exhibits relatively low resistance. On the other hand,the second part 20 b has a lower dopant concentration and a smallerjunction depth than the first part 20 a. Consequently, the second part20 b exhibits higher resistance than the first part 20 a.

As described above, in this embodiment of the present invention, thefirst part 20 a having relatively low resistance may be formed at a partadjacent to the first electrode 42 to reduce contact resistance with thefirst electrode 42. In addition, the second part 20 b having relativelyhigh resistance may be formed at a part corresponding to a lightreceiving region, upon which light is incident, between the firstelectrodes 42 to constitute a shallow emitter. Consequently, it ispossible to improve current density of the solar cell 100. That is, inthis embodiment of the present invention, the first conductive region 20may have a selective structure, thereby maximizing the efficiency of thesolar cell 100.

In addition, the second conductive region 30 may include a first part 30a formed adjacent to (e.g. in contact with) the second electrode 44 anda second part 30 b formed at a region where the second electrode 44 isnot positioned. The first part 30 a has a relatively high dopantconcentration and a relatively large junction depth. Consequently, thefirst part 30 a exhibits relatively low resistance. On the other hand,the second part 30 b has a lower dopant concentration and a smallerjunction depth than the first part 30 a. Consequently, the second part30 b exhibits higher resistance than the first part 30 a.

As described above, in this embodiment of the present invention, thesecond part 30 a having relatively low resistance may be formed at apart adjacent to the second electrode 44 to reduce contact resistancewith the second electrode 44. In addition, the second part 30 b havingrelatively high resistance may be formed at a part corresponding to aregion, upon which light is incident, between the second electrodes 44to prevent recombination between holes and electrons. Consequently, itis possible to improve current density of the solar cell 100. That is,in this embodiment of the present invention, the second conductiveregion 30 may have a selective structure, thereby maximizing theefficiency of the solar cell 100.

However, the embodiments of the present invention are not limitedthereto. The first conductive region 20 and/or the second conductiveregion 30 may have a homogeneous structure as shown in FIG. 1.Alternatively, the second conductive region 30 may have a localstructure which does not include the second part 30 b but includes onlythe second part 30 a.

FIG. 9 is a sectional view showing a further example of the solar cellmanufactured using the manufacturing method of the solar cell accordingto the embodiment of the present invention.

Referring to FIG. 9, the solar cell according to this embodiment isconfigured such that conductive regions 20 and 30 are formed on asemiconductor substrate 110 separately from the semiconductor substrate110 and have a crystalline structure different from that of thesemiconductor substrate 110. Consequently, the semiconductor substrate110 may not include the conductive regions 20 and 30 but include only abase region 10.

More specifically, a first tunneling layer 52 may be formed on the frontsurface of the semiconductor substrate 110, and the first conductiveregion 20 may be positioned on the first tunneling layer 52.

The first tunneling layer 52 may improve the passivation characteristicsof the front surface of the semiconductor substrate 110, and generatedcarriers may be smoothly transmitted due to a tunneling effect. Thefirst tunneling layer 52 may include various materials, such as anitride, a semiconductor, and a conductive polymer, which are capable oftunneling the carriers. For example, the first tunneling layer 52 mayinclude a silicon oxide, a silicon nitride, a silicon oxide nitride, anintrinsic amorphous semiconductor (e.g. intrinsic amorphous silicon),and an intrinsic polycrystalline semiconductor (e.g. intrinsicpolycrystalline silicon). In an instance in which the first tunnelinglayer 52 includes an intrinsic amorphous semiconductor, thesemiconductor substrate 110 may be easily manufactured using a simplemanufacturing process since the first tunneling layer 52 exhibitscharacteristics similar to those of the semiconductor substrate 110,thereby more effectively improving the surface characteristics of thesemiconductor substrate 110. Consequently, it is possible to preventsurface recombination which may be generated at the surface of thesemiconductor substrate 110, thereby improving the passivationcharacteristics of the semiconductor substrate 110.

The first tunneling layer 52 may be formed throughout the front surfaceof the semiconductor substrate 110. Consequently, the entirety of thefront surface of the semiconductor substrate 110 may be passivated, andthe first tunneling layer 52 may be easily formed without additionalpatterning.

In order to sufficiently achieve the tunneling effect, the firsttunneling layer 52 may have a thickness of 5 nm or less. Specifically,the first tunneling layer 52 may have a thickness of 0.5 to 5 nm (e.g. 1to 4 nm). If the thickness of the first tunneling layer 52 is greaterthan 5 nm, tunneling may not be satisfactorily achieved with the resultthat the solar cell 100 may not be operated. On the other hand, if thethickness of the first tunneling layer 52 is less than 0.5 nm, it may bedifficult to form the first tunneling layer 52 such that the firsttunneling layer 52 has desired quality. In order to further improve thetunneling effect, the first tunneling layer 52 may have a thickness of 1to 4 nm. However, the embodiments of the present invention are notlimited thereto. The thickness of the first tunneling layer 52 may bevariously changed.

The first conductive region 20 of a first conductive type, which isopposite to that of the semiconductor substrate 110 or the base region10, may be formed on the first tunneling layer 52. The first conductiveregion 20 may form a pn junction (e.g. a pn tunnel junction) togetherwith the semiconductor substrate 110 or the base region 10 to constitutean emitter region for generating carriers through photoelectricconversion.

The first conductive region 20, which is formed on the first tunnelinglayer 52 separately from the semiconductor substrate 110, may have acrystalline structure different from that of the semiconductor substrate110. That is, the first conductive region 20 may include an amorphoussemiconductor (e.g. amorphous silicon), a micro-crystallinesemiconductor (e.g. micro-crystalline silicon), or a polycrystallinesemiconductor (e.g. polycrystalline silicon), which may be easily formedon the first conductive region 20 using various methods, such asdeposition. Consequently, the first conductive region 20 may be formedof an amorphous semiconductor (e.g. amorphous silicon), amicro-crystalline semiconductor (e.g. micro-crystalline silicon), or apolycrystalline semiconductor (e.g. polycrystalline silicon) having afirst conductive dopant. The first conductive dopant may be included ina semiconductor layer when the semiconductor layer is formed for formingthe first conductive region 20 or may be included in the semiconductorlayer using various doping methods, such as thermal diffusion, ioninjection, and laser doping, after the semiconductor layer is formed.

Similarly, a second tunneling layer 54 may be formed on the back surfaceof the semiconductor substrate 110, and the second conductive region 30may be positioned on the second tunneling layer 54. The material andthickness of the second tunneling layer 54 are similar to those of thefirst tunneling layer 52, and therefore a detailed description thereofwill be omitted. The material and crystalline structure of the secondconductive region 30 are identical to or similar to those of the firstconductive region 20 except that the second conductive region 30 has afirst conductive dopant, and therefore a detailed description thereofwill be omitted.

In this embodiment of the present invention, a first transparentconduction layer 421 may be formed between a first electrode 42 and thefirst conductive region 20, and a second transparent conduction layer441 may be formed between a second electrode 44 and the secondconductive region 30.

In an instance in which the tunneling layers 52 and 54 are formed on thefront surface of the semiconductor substrate 110, and then theconductive regions 20 and 30 are formed on the tunneling layers 52 and54 as described above, it is possible to greatly improve the passivationcharacteristics of the semiconductor substrate 110. In addition, it ispossible to reduce the thickness of the semiconductor substrate 110,which is expensive, thereby reducing manufacturing cost. Furthermore, itis possible to manufacture the solar cell 100 at a low processtemperature. Since the crystallinity of the conductive regions 20 and 30is relatively low, however, carrier mobility may be relatively low. Inthis embodiment of the present invention, therefore, the firsttransparent conduction layer 421 is formed between the first electrode42 and the first conductive region 20, and the second transparentconduction layer 441 is formed between the second electrode 44 and thesecond conductive region 30, thereby reducing resistance when thecarriers move in a horizontal direction.

The first transparent conduction layer 421 may be formed throughout thefirst conductive region 20, which may mean that not only the firsttransparent conduction layer 421 may cover the entirety of the firstconductive region 20 without an empty space or an empty region but alsothe first transparent conduction layer 421 may not be formed at aportion of the first conductive region 20. In an instance in which thefirst transparent conduction layer 421 is formed throughout the firstconductive region 20, the carriers may easily reach the first electrode42 via the first transparent conduction layer 421, thereby reducingresistance in the horizontal direction.

Since the first transparent conduction layer 421 is formed throughoutthe first conductive region 20, the first transparent conduction layer421 may be formed of a light transmissive material. That is, the firsttransparent conduction layer 421 may be formed of a transparentconductive material for easily moving the carriers while transmittinglight. Consequently, transmission of light is not blocked even in aninstance in which the first transparent conduction layer 421 is formedthroughout the first conductive region 20. For example, the firsttransparent conduction layer 421 may include an indium tin oxide (ITO)or a carbon nano tube (CNT). However, the embodiments of the presentinvention are not limited thereto. The first transparent conductionlayer 421 may include various other materials.

The material and shape of the second transparent conduction layer 441may be similar to those of the first transparent conduction layer 421,and therefore a detailed description thereof will be omitted.

On the first transparent conduction layer 421 may be positioned ananti-reflection film 24 having an opening 102, via which the firstelectrode 42 is connected to the first transparent conduction layer 421.The anti-reflection film 24 may include a dielectric material having alower refractive index than the first transparent conduction layer 421.In an instance in which the anti-reflection film 24 having a lowerrefractive index than the first transparent conduction layer 421 isformed on the first transparent conduction layer 421 as described above,the first transparent conduction layer 421 and the anti-reflection film24 may function as a double anti-reflection film. In addition, in aninstance in which the anti-reflection film 24 includes a dielectricmaterial, the anti-reflection film 24 may be used as a mask layer whenthe first electrode 42 is formed so as to have a pattern. In addition,the anti-reflection film 24 may also function as a protective layer forprotecting the first transparent conduction layer 421.

In this embodiment of the present invention, the anti-reflection film 24includes hydrogen. In this case, the anti-reflection film 24 mayfunction as a hydrogen source at the post-processing operation (ST50).The material of the anti-reflection film 24 may be identical to orsimilar to that of the first passivation film 22 or the anti-reflectionfilm 24 previously described with reference to FIG. 1, and the hydrogencontent of the anti-reflection film 24 may be equal to or similar tothat of the first passivation film 22 previously described withreference to FIG. 1.

In the above description and the figures, the anti-reflection film 24positioned on the front surface of the semiconductor substrate 110 isillustrated as including hydrogen. However, the embodiments of thepresent invention are not limited thereto. For example, a dielectricfilm (e.g. the second passivation film 32 shown in FIG. 1 or anadditional anti-reflection film) may be further positioned on the backsurface of the semiconductor substrate 110, and the dielectric filmpositioned on the back surface of the semiconductor substrate 110 mayinclude hydrogen.

The semiconductor substrate 110 including the base region 10 may be of ap-type having boron. In this case, it is possible to greatly improve thecharacteristics of the solar cell 100 due to the effects obtained by thepost-processing operation (ST50). However, the embodiments of thepresent invention are not limited thereto. For example, thesemiconductor substrate 110 may have a different dopant, or may be of ann-type. Even in this case, it is possible to achieve the effectsobtained by the post-processing operation (ST50).

Hereinafter, the embodiments of the present invention will be describedin more detail with reference to an experimental example. Theexperimental example is provided merely to describe the embodiments ofthe present invention in more detail and thus does not restrict theembodiments of the present invention.

Experimental Example

A solar cell having a structure as shown in FIG. 1 was manufacturedusing a semiconductor substrate including a p-type base region havingboron. At this time, a passivation film included about 10²⁰ ea/cm³ ofhydrogen, and a peak temperature was 700° C. and process time was 10 secat an electrode firing operation. At the electrode firing operation, ahydrogen diffusion process was simultaneously carried out.

Subsequently, a preliminary heat treatment process was carried out at atemperature of about 200° C. for 5 minutes. A main processing processwas carried out for a plurality of solar cells while changing thetemperature, the light intensity, and the time, within a temperaturerange of 200 to 700° C. and a light intensity range of 10⁴ mW/cm² to8×10⁴ mW/cm² to measure an output loss of each solar cell. Based on themeasured output loss values of the solar cells, temperature and lightintensity exhibiting the same output losses were mapped as shown in FIG.10, and light intensity and time exhibiting the same output losses weremapped as shown in FIG. 11.

In FIG. 10, dotted lines L1, L2, L3, L4, and L5 interconnecting pointsindicating the same output losses are shown. The output loss is reducedin order of L5, L4, L3, L2, and L1. In addition, the minimum valuesI_(min) of the light intensity calculated according to Equation 1 attemperatures of 300° C., 400° C., 500° C., 600° C., and 700° C. areshown as quadrangular points, and a line interconnecting thequadrangular points is shown as a solid line. In FIG. 11, dotted linesL11, L12, L13 interconnecting points indicating the same output lossesare shown. The output loss is reduced in order of L13, L12, and L11.

Referring to FIG. 10, it can be seen that it is possible to reduce theoutput loss of the solar cell only when light having a predeterminedlight intensity or more is supplied at a uniform temperature and that itis necessary to also increase the light intensity as the temperatureincreases in order to reduce the output loss of the solar cell. It canalso be seen that in an instance in which the light intensity is greaterthan that shown as the quadrangular point at each temperature, theoutput loss is reduced. Consequently, it can be seen that in an instancein which the main processing process is carried out at the temperatureand the light intensity according to equations defined by theembodiments of the present invention, it is possible to actually reducethe output loss of the solar cell.

Referring to FIG. 11, it can be seen that in an instance in which thelight intensity is high, it is possible to greatly reduce the outputloss even when the main processing process is carried out during a shortprocess time. This coincides with the time-light intensity equationsdefined in the embodiments of the present invention.

At least the main processing process (ST56) (see FIG. 3) of thepost-processing operation (ST50) (see FIG. 3) of the manufacturingmethod of the solar cell 100 may be carried out by a post-processingapparatus 200 of a solar cell according to an embodiment of the presentinvention (hereinafter, simply referred to as a “post-processingapparatus”). Hereinafter, a post-processing apparatus 200 according toan embodiment of the present invention will be described in detail.

FIG. 12 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to an embodiment ofthe present invention.

Referring to FIG. 12, the post-processing apparatus 200 of the solarcell according to this embodiment basically includes a main section 220,having a light source unit 222 and a first heat source unit 224, forcarrying out the main period (ST562) (see FIG. 5) for the semiconductorsubstrate 110 (see FIG. 1) or the solar cell 100 including thesemiconductor substrate 110. A temperature rising section 210 forcarrying out the temperature rising period (ST561) (see FIG. 5) may bepositioned before the main section 220, and a cooling section 230 forcarrying out the cooling period (ST563) (see FIG. 5) may be positionedafter the main section 220.

In this embodiment of the present invention, the temperature risingsection 210, the main section 220, and the cooling section 230 aresequentially arranged. In a state in which the solar cell 100 is placedon a conveying unit, such as a conveyer belt 202, the conveyer belt 202may move such that the solar cell 100 placed on the conveyer belt 202sequentially passes through the temperature rising section 210, the mainsection 220, and the cooling section 230. Consequently, the process ofthe temperature rising period (ST561) is carried out for the solar cell100 in the temperature rising section 210. Subsequently, the process ofthe main period (ST562) is carried out for the solar cell 100 in themain section 220. Subsequently, the process of the cooling period(ST563) is carried out for the solar cell 100 in the cooling section230.

The conveyer belt 202 may have various structures and mechanisms inwhich the solar cell 100 can be stably placed on the conveyer belt 202.For example, the conveyer belt 202 may have a mesh structure in whichlight and heat can be more effectively provided to the solar cell 100,and the solar cell 100 can be maintained at a uniform temperature. In anexample, a worktable 204 shown in FIG. 14 may extend to constitute theconveyer belt 202. The shape of the worktable 204 will hereinafter bedescribed in more detail with reference to FIG. 14. However, theembodiments of the present invention are not limited thereto. Theconveyer belt 202 may have various structures.

For example, the conveyer belt 202 may have a moving speed of 50 mm/minto 1000 mm/min. At this moving speed, the solar cell 100 can be movedwithout impact or damage to the solar cell 100, and the process of thetemperature rising period, the process of the main period (ST562), andthe process of the cooling period (ST563) can be carried out for thesolar cell 100 during desired time.

However, the embodiments of the present invention are not limitedthereto. The moving speed of the conveyer belt 202 may be variouslychanged. For example, in an instance in which an additional heat sourceunit 216 is positioned in the temperature rising section 210 toaccelerate the increase of temperature, the moving speed of the conveyerbelt 202 may be increased. Alternatively, in an instance in which thesize of the temperature rising section 210, the main section 220, or thecooling section 230 is large and thus the process can be carried outduring a sufficient time even when the moving speed of the conveyer belt202 is high, the moving speed of the conveyer belt 202 may be increased.On the other hand, in an instance in which the size of the temperaturerising section 210, the main section 220, or the cooling section 230 issmall, the moving speed of the conveyer belt 202 may be decreased suchthat the process can be carried out during a sufficient time. Inaddition, the moving speeds of the conveyer belt 202 in the temperaturerising section 210, the main section 220, and the cooling section 230may be different from each other. Various other modifications are alsopossible.

In an instance in which the process is carried out in the temperaturerising section 210, the main section 220, and the cooling section 230based on an in-line process using the conveyer belt 202 as describedabove, it is possible to increase output due to the continuous process.In this embodiment of the present invention, the conveyer belt 202 isused as an example of the conveying means for the in-line process.However, the embodiments of the present invention are not limitedthereto. Various structures and mechanisms that are capable of carryingout the in-line process may be used.

As described above, in this embodiment of the present invention, thein-line process using the conveyer belt is carried out. However, theembodiments of the present invention are not limited thereto. Forexample, the post-processing apparatus 200 may have a batch structure inwhich the process can be carried out in a state in which the solar cell100 is not moved, i.e. the solar cell 100 is fixed at a specificposition, which will be described in detail with reference to FIGS. 13to 16.

Hereinafter, the main section 220 in which the basic process, i.e. themain period (ST562), of the main processing process (ST56) is carriedout will be described in detail, and then the temperature rising section210 and the cooling section 230 will be described in detail.

As previously described, in the main period (ST562), the solar cell 100(or the semiconductor substrate 110) is heat-treated at a uniformtemperature in a state in which light having a uniform light intensityis supplied to the solar cell 100. To this end, the main section 220includes a light source unit 222 for supplying a light having a uniformlight intensity to the solar cell 100 and a heat source unit (or a firstheat source unit) 224 for heating the solar cell 100 at a uniformtemperature.

The light source unit 222 functions to supply light having a uniformlight intensity to the solar cell 100. As previously described, lighthaving a light intensity of 1.7×10² mW/cm² to 10⁵ mW/cm² is needed inthe main period (ST562). Consequently, the light source unit 222 maysupply light having a light intensity of 1.7×10² mW/cm² to 10⁵ mW/cm².

At this time, various methods of adjusting the light intensity of thelight source unit 222 may be used to supply light having light intensitynecessary for the main period (ST562). That is, it is possible to adjustthe number, kind, and output of light sources 222 a and 222 bconstituting the light source unit 222 or to change the distance betweenthe light sources 222 a and 222 b and the solar cell 100.

In this embodiment of the present invention, the light source unit 222,including the light sources 222 a and 222 b, may supply a sufficientamount of light to the solar cell 100. However, the embodiments of thepresent invention are not limited thereto. In an instance in which lighthaving a high light intensity is not needed, only one of the lightsources 222 a and 222 b may be provided.

Furthermore, in this embodiment of the present invention, each of thelight sources 222 a and 222 b may be constituted by a plasma lightingsystem (PLS) for supplying light based on plasma emission. In the plasmalighting system, a bulb is filled with a specific gas, anelectromagnetic wave, such as a microwave generated by a magnetron, oran incident beam is applied to the bulb to ionize the gas in the bulb(i.e. to generate plasma), and light is emitted from the plasma.

The plasma lighting system does not use an electrode, a filament, andmercury, which are components of a conventional lighting system.Consequently, the plasma lighting system is environmentally friendly andexhibits a semi-permanent lifetime. In addition, the plasma lightingsystem has a very excellent luminous flux maintenance factor. For thisreason, the change in quantity of light is small even when the plasmalighting system is used based on super luminous flux for a long time.Furthermore, the plasma lighting system exhibits high thermal resistanceand thus high thermal stability. Consequently, the plasma lightingsystem may be used in a space in which the heat source unit 224 ispositioned. In addition, the plasma lighting system may emit lighthaving a sufficient light intensity. For reference, another lightsource, such as a light emitting diode, exhibits low thermal resistancewith the result that it is difficult to use the light emitting diodetogether with the heat source unit 224, and the light emitting diodeemits only light having low light intensity. In addition, the plasmalighting system may emit almost uniform continuous light over allwavelengths of visible light. Consequently, the plasma lighting systemmay supply light similar to solar light. In this embodiment of thepresent invention, a compound of indium (In) and bromine (Br) may beused as the gas filling the bulb of the plasma lighting system. In thiscase, the plasma lighting system may have a spectrum more similar tothat of solar light than in an instance in which sulfur is used as thegas filling the bulb of the plasma lighting system. In an instance inwhich light having a spectrum similar to that of the solar light issupplied, it is possible to carry out the main processing process (ST56)under conditions similar to those of the solar light, therebyeffectively preventing output loss, which may be caused due to the solarlight, through the main processing process (ST56).

In this embodiment of the present invention, a cover substrate 223positioned on the front surface (i.e. light emitting surface) of each ofthe light sources 222 a and 222 b may include a base substrate 223 a anda plurality of layers 223 b, positioned on the base substrate 223 a,including materials having different refractive indices.

The base substrate 223 a may be formed of a light transmissive materialhaving a sufficient strength to protect the light sources 222 a and 222b. For example, the base substrate 223 a may be formed of glass.

The layers 223 b, which are configured by stacking layers havingdifferent refractive indices, may block undesired light. For example,the layers 223 b may be formed of oxide materials having differentrefractive indices. In this case, the layers 223 b may block lighthaving a wavelength of less than 600 nm (specifically, 400 nm to 600 nm)and greater than 1000 nm. Various materials and stack structures of thelayers 223 b may be applied so long as the layers 223 b can block lighthaving a wavelength of less than 600 nm (specifically, 400 nm to 600 nm)and greater than 1000 nm.

In the figure, the layers 223 b are illustrated as being positioned atthe outer surface of the base substrate 223 a. However, the embodimentsof the present invention are not limited thereto. For example, thelayers 223 b may be positioned at the inner surface of the basesubstrate 223 a. Alternatively, the layers 223 b may be positioned atboth the inner surface and the outer surface of the base substrate 223a.

In this embodiment of the present invention, the outer surface of thecover substrate 223 (i.e. the surface of the cover substrate 223opposite to the solar cell 100) may be flat. As a result, light may beuniformly supplied to the solar cell 100 through the cover substrate 223such that the light can be uniformly distributed over the solar cell100. On the other hand, a light source of a general plasma lightingsystem is used outside. For this reason, a concave cover substrate isgenerally used to improve straightness of light.

Consequently, the light emitted from the light sources 222 a and 222 bto the solar cell 100 may have a wavelength of 600 nm to 1000 nm. In aninstance in which an ultraviolet light portion of the light emitted fromthe light sources 222 a and 222 b is blocked as described above, it ispossible to minimize lowering in passivation characteristics of thepassivation film 22 (see FIG. 1) and/or 32 (see FIG. 8) which may becaused when ultraviolet light is emitted to the solar cell 100. Inaddition, in an instance in which an infrared light portion of the lightemitted from the light sources 222 a and 222 b is blocked, it ispossible to minimize an amount of heat supplied from the light sources222 a and 222 b to the solar cell 100. On the other hand, in an instancein which the light sources 222 a and 222 b emit infrared light to thesolar cell 100, the light source unit 222 as well as the heat sourceunit 224 may supply heat to the solar cell 100 with the result that itmay be difficult to maintain the solar cell 100 at a desiredtemperature. In this embodiment of the present invention, therefore, itis possible to maximally prevent the light source unit 222 fromaffecting the temperature of the solar cell 100 such that thetemperature of the solar cell 100 can be independently controlled by theheat source unit 224.

In this embodiment of the present invention, the cover substrate 223constituting each of the light sources 222 a and 222 b may block aportion of the light such that only an efficient portion of the lightfor the main period (ST562) can be supplied to the solar cell 100.Consequently, it is possible to maximize the effects of the main period(ST562) through such a simple structure. However, the embodiments of thepresent invention are not limited thereto. For example, a filter may bedisposed between the light sources 222 a and 222 b and the solar cell100 for blocking a portion of the light.

In this embodiment of the present invention, the light sources 222 a and222 b, each of which includes the plasma lighting system, are used.Consequently, it is possible to stably supply light having a desiredlight intensity to the solar cell 100. However, the embodiments of thepresent invention are not limited thereto. For example, one of the lightsources 222 a and 222 b in the main section 220 may be constituted bythe plasma lighting system, and the other of the light sources 222 a and222 b may be constituted by another type of light source. Various othermodifications are also possible.

In the main section 220, the heat source unit 224 may supply anappropriate amount of heat to the solar cell 100 such that the solarcell 100 has a desired temperature. Various mechanisms, structures, andshapes of the heat source unit 224 may be applied.

In this embodiment of the present invention, the heat source unit 224,including a plurality of heat sources 224 a and 224 b, may supply asufficient amount of heat to the solar cell 100. However, theembodiments of the present invention are not limited thereto. Only oneof the heat sources 224 a and 224 b may be provided in consideration ofthe structure, mechanism, and shape of the heat sources 224 a and 224 band heat treatment temperature of the solar cell 100.

For example, each of the heat sources 224 a and 224 b constituting theheat source unit 224 may be an ultraviolet lamp. In an example, each ofthe heat sources 224 a and 224 b may be a halogen lamp. In anotherexample, a coil heater may be used as each of the heat sources 224 a and224 b. In an instance in which an ultraviolet lamp, such as a halogenlamp, is used as each of the heat sources 224 a and 224 b, it ispossible to more rapidly increase the temperature of the solar cell 100than in an instance in which the coil heater is used. On the other hand,in an instance in which a coil heater is used as each of the heatsources 224 a and 224 b, it is possible to reduce facility costs.

In this embodiment of the present invention, the heat source unit 224may be spaced apart from the solar cell 100 or the conveyor belt 202, onwhich the solar cell 100 is placed, such that the heat source unit 224can heat the solar cell 100 in an atmospheric heating fashion in whichthe heat source unit 224 heats air in the main section 220 by radiation.As a result, it is possible to minimize damage to the solar cell 100caused by the heat source unit 224 and generation of heat from a localpart of the solar cell 100. For example, in an instance in which each ofthe heat sources 224 a and 224 b of the heat source unit 224 is anultraviolet lamp, the passivation characteristics of the passivationfilms 22 and 32 may be lowered by ultraviolet light emitted from theheat sources 224 a and 224 b. In addition, in a case in which the heatsources 224 a and 224 b of the heat source unit 224 directly contacteach other, the heat sources 224 a and 224 b may locally heat the solarcell 100 due to a process error with the result that a portion of thesolar cell 100 may be heated to an undesired temperature.

However, the embodiments of the present invention are not limitedthereto. For example, the solar cell 100 may be heated by conductioninstead of atmospheric heating, which will hereinafter be described indetail with reference to FIG. 13.

As described above, in the main period (ST562), the solar cell 100 isheat-treated in a state in which light is supplied from the light sourceunit 222 and heat is supplied from the heat source unit 224 such thatthe solar cell 100 is maintained at a uniform temperature. In thisembodiment of the present invention, the light source unit 222 and theheat source unit 224 may supply light and heat to the solar cell 100 ina state in which the light source unit 222 and the heat source unit 224are separated from each other. That is, the light sources 222 a and 222b constituting the light source unit 222 are adjacent to each other, andthe heat sources 224 a and 224 b constituting the heat source unit 224are adjacent to each other such that the light sources 222 a and 222 bconstituting the light source unit 222 and the heat sources 224 a and224 b constituting the heat source unit 224 are spaced apart from eachother. In this state, the light source unit 222 and the heat source unit224 may supply light and heat to the solar cell 100, thereby minimizingthe light source unit 222 and the heat source unit 224 from affectingeach other.

For example, in the main section 220, the light source unit 222 may bepositioned at one side of the solar cell 100, and the heat source unit224 may be positioned at the other side of the solar cell 100 (forexample, at the other side of the solar cell 100 opposite to the oneside of the solar cell 100). As a result, light and heat from the lightsource unit 222 and the heat source unit 224 may be effectively suppliedto the solar cell 100 in a state in which interference between the lightsource unit 222 and the heat source unit 224 is minimized.

In an example, the light source unit 222 may be positioned at the upperside of the solar cell 100 (i.e. the upper side of the conveyor belt202), and the heat source unit 224 may be positioned at the lower sideof the solar cell 100 (i.e. the lower side of the conveyor belt 202). Inan instance in which the light source unit 222 is positioned at thelower side of the conveyor belt 202, a portion of light emitted from thelight source unit 222 is blocked by the conveyor belt 202 with theresult that the light may not be effectively supplied to the solar cell100. On the other hand, in an instance in which the heat source unit 224is positioned at the lower side of the conveyor belt 202, it is possibleto supply a sufficient amount of heat to the solar cell 100 byatmospheric heating. In this embodiment of the present invention,therefore, the light source unit 222 is positioned at the upper side ofthe solar cell 100 or the conveyor belt 202, and the heat source unit224 is positioned at the lower side of the solar cell 100 or theconveyor belt 202). However, the embodiments of the present inventionare not limited thereto. Positions of the light source unit 222 and theheat source unit 224 may be changed.

The temperature rising section 210, which is positioned before the mainsection 220, is a section for carrying out the temperature rising period(ST561) of the main processing process (ST56). That is, the temperaturerising section 210 is a section for preliminarily heating the solar cell100 at a temperature necessary for the main period (ST562) of the mainprocessing process (ST56). To this end, the temperature rising section210 includes a heat source unit (or a second heat source unit) 214 forsupplying heat to the solar cell 100.

The heat source unit 214 of the temperature rising section 210 may bepositioned at the same side (e.g. the lower side) as the heat sourceunit 224 of the main section 220. In an instance in which the heatsource unit 214 of the temperature rising section 210 and the heatsource unit 224 of the main section 220 are positioned at one side asdescribed above, the structure of the post-processing apparatus 200 maybe simplified. However, the embodiments of the present invention are notlimited thereto. The heat source unit 214 of the temperature risingsection 210 and the heat source unit 224 of the main section 220 may bevariously modified.

In the temperature rising section 210, the heat source unit 214 maysupply an appropriate amount of heat to the solar cell 100 such that thesolar cell 100 can be preliminarily heated to a desired temperature.Various mechanisms, structures, and shapes of the heat source unit 214may be applied.

In this embodiment of the present invention, the heat source unit 214,including a plurality of heat sources 214 a and 214 b, may supply asufficient amount of heat to the solar cell 100. However, theembodiments of the present invention are not limited thereto. Only oneof the heat sources 214 a and 214 b may be provided in consideration ofthe structure, mechanism, and shape of the heat sources 214 a and 214 band heat treatment temperature of the solar cell 100.

For example, each of the heat sources 214 a and 214 b constituting theheat source unit 214 may be an ultraviolet lamp. In an example, each ofthe heat sources 214 a and 214 b may be a halogen lamp. In anotherexample, a coil heater may be used as each of the heat sources 214 a and214 b. In an instance in which an ultraviolet lamp, such as a halogenlamp, is used as each of the heat sources 214 a and 214 b, it ispossible to more rapidly increase the temperature of the solar cell 100than in an instance in which a coil heater is used. On the other hand,in an instance in which a coil heater is used as each of the heatsources 214 a and 214 b, it is possible to reduce facility costs.

In this embodiment of the present invention, the heat source unit 214may be spaced apart from the solar cell 100 or the conveyor belt 202, onwhich the solar cell 100 is placed, such that the heat source unit 214can heat the solar cell 100 in an atmospheric heating fashion in whichthe heat source unit 214 heats air in the temperature rising section 210by radiation. As a result, it is possible to minimize damage to thesolar cell 100 caused by the heat source unit 214 and generation of heatfrom a local part of the solar cell 100.

The temperature rising section 210 may further include an additionalheat source unit 216 positioned at the side opposite to the heat sourceunit 214 (e.g. the upper side of the solar cell 100 or the conveyor belt202). In an instance in which the heat source unit 214 and theadditional heat source unit 216 supply heat to the solar cell 100 at theopposite sides of the solar cell 100 in the temperature rising section210 as described above, it is possible to increase the temperaturerising speed of the solar cell 100. The additional heat source unit 216may be adjacent to the entrance of the temperature rising section 210,through which the solar cell 100 is introduced into the temperaturerising section 210. As a result, the temperature rising speed of thesolar cell 100 in the temperature rising section 210 may be increased,thereby improving productivity.

Various mechanisms, structures, and shapes of the additional heat sourceunit 216 may be applied. In this embodiment of the present invention,the additional heat source unit 216 includes one heat source. However,the embodiments of the present invention are not limited thereto. Theadditional heat source unit 216 may include a plurality of heat sourcesin consideration of the structure, mechanism, and shape of theadditional heat source unit 216 and heat treatment temperature of thesolar cell 100.

In addition, an additional light source (or a first additional lightsource) 212 may be also positioned in the temperature rising section210. When it is necessary to supply a larger amount of light in the mainperiod (ST562) carried out in the main section 220 or when it isnecessary to increase the process time of the main period (ST562), theadditional light source 212 of the temperature rising section 210 may beprovided to carry out the same process as that of the main period(ST562) in the temperature rising section 210. That is, a portion of thetemperature rising section 210 may be used as the main section 220 asneeded, which will hereinafter be described in more detail whendescribing a partition wall unit 240.

The additional light source 212 may be positioned in the temperaturerising section 210 in a state in which the additional light source 212is adjacent to the main section 220 such that a portion of thetemperature rising section 210 can be easily used as the main section220. Referring to FIG. 5, a portion of the temperature rising period(ST561) adjacent to the main period (ST562) has a temperature equal toor similar to that of the main period (ST562). Consequently, a portionof the temperature rising section 210 may be used as the main section220.

Various mechanisms, structures, and shapes of the additional lightsource 212 may be applied. For example, the additional light source 212may be constituted by the same plasma lighting system as each of thelight sources 222 a and 222 b of the light source unit 222 and may havea structure identical to or similar to that of each of the light sources222 a and 222 b of the light source unit 222. In this embodiment of thepresent invention, one additional light source 212 is provided. However,the embodiments of the present invention are not limited thereto. Aplurality of additional light sources 212 may be provided inconsideration of the structure, mechanism, and shape of each of theadditional light sources 212 and required intensity of light.

However, the additional light source 212 is not a requisite. Since lightis not fundamentally supplied to the solar cell 100 in the temperaturerising period (ST561) carried out in the temperature rising section 210,therefore, the temperature rising section 210 may carry out only thetemperature rising period (ST561) without the provision of theadditional light source 212.

Between the temperature rising section 210 and the main section 220 maybe positioned a partition wall unit 240 for partitioning or defining thetemperature rising section 210 and the main section 220. The partitionwall unit 240 functions to prevent generation of undesired combinationin the temperature rising period (ST561) which may be caused by lightsupplied from the main section 220 to the solar cell 100 positioned inthe temperature rising section 210.

Various structures of the partition wall unit 240 may be applied. Forexample, the partition wall unit 240 may be a structure (e.g. a metalplate or a dielectric plate) for physically partitioning the temperaturerising section 210 and the main section 220. The partition wall unit 240may be installed such that the partition wall unit 240 can be movedupward and downward. When it is necessary to supply a larger amount oflight in the main period (ST562) carried out in the main section 220 orwhen it is necessary to increase the process time of the main period(ST562), therefore, the partition wall unit 240 may be moved upward suchthat the additional light source 212 of the temperature rising section210 can carry out the same process as that of the main period (ST562) inthe temperature rising section 210. When it is not necessary to use theadditional light source 212, the partition wall unit 240 may be moveddownward to prevent introduction of light from the main section 220 tothe temperature rising section 210.

The cooling section 230, which is positioned after the main section 220,is a section for carrying out the cooling period (ST563) of the mainprocessing process (ST56). That is, the cooling section 230 is a sectionfor cooling the solar cell 100 having passed the main period (ST562) ofthe main processing process (ST56). For this reason, the cooling section230 includes no heat source unit.

The solar cell 100 may be slowly cooled by air or more rapidly cooledusing an additional cooling apparatus. However, the embodiments of thepresent invention are not limited thereto. Various structures forcooling may be applied.

An additional light source 232 may be also positioned in the coolingsection 230. When it is necessary to supply a larger amount of light inthe main period (ST562) carried out in the main section 220 or when itis necessary to increase the process time of the main period (ST562),the additional light source 232 of the cooling section 230 may beprovided to carry out the same process as that of the main period(ST562) in the cooling section 230. That is, a portion of the coolingsection 230 may be used as the main section 220 as needed. Theadditional light source 232 may be positioned in the cooling section 230in a state in which the additional light source 232 is adjacent to themain section 220 such that a portion of the cooling section 230 can beeasily used as the main section 220.

Various mechanisms, structures, and shapes of the additional lightsource 232 may be applied. For example, the additional light source 232may be constituted by the same plasma lighting system as each of thelight sources 222 a and 222 b of the light source unit 222 and may havea structure identical to or similar to that of each of the light sources222 a and 222 b of the light source unit 222. In this embodiment of thepresent invention, one additional light source 232 is provided. However,the embodiments of the present invention are not limited thereto. Aplurality of additional light sources 212 may be provided inconsideration of the structure, mechanism, and shape of each of theadditional light sources 212 and required intensity of light.

However, the additional light source 232 is not a requisite. Since it isnot necessary to fundamentally supply heat to the solar cell 100 in thecooling period (ST563) carried out in the cooling section 230,therefore, the cooling section 230 may carry out only the cooling period(ST563) without the provision of the additional light source 232.

A partition wall unit may also be positioned between the main section220 and the cooling section 230. This partition wall unit may have astructure identical to or similar to that of the partition wall unitpositioned between the temperature rising section 210 and the mainsection 220. Since the solar cell 100 is little affected even when lightis introduced into the cooling section 230, however, no partition wallunit may be positioned between the main section 220 and the coolingsection 230. As a result, it is possible to simplify the structure ofthe post-processing apparatus 200.

In this embodiment of the present invention, air curtain members 252,254, 256, and 258 may be installed at at least one of the interfacesdefined among the temperature rising section 210, the main section 220,and the cooling section 230. For example, each of the air curtainmembers 252, 254, 256, and 258 may have a bar shape with a plurality ofair injection holes, through which air is supplied. However, theembodiments of the present invention are not limited thereto. Variousstructures and mechanisms of the air curtain members 252, 254, 256, and258 may be applied.

In this embodiment of the present invention, the first air curtainmember 252 may be positioned at the entrance of the temperature risingsection 210, the second air curtain member 254 may be positioned betweenthe temperature rising section 210 and the main section 220, the thirdair curtain member 256 may be positioned between the main section 220and the cooling section 230, and the fourth air curtain member 258 maybe positioned at the exit of the cooling section 230. The second aircurtain member 254 may be installed at the partition wall unit 240positioned between the temperature rising section 210 and the mainsection 220. Alternatively, the second air curtain member 254 may beinstalled separately from the partition wall unit 240. In an instance inwhich a partition wall unit is provided between the main section 220 andthe cooling section 230, the third air curtain member 256 may also beinstalled at the partition wall unit. Alternatively, the third aircurtain member 256 may be installed separately from the partition wallunit. Various other modifications are also possible.

The first air curtain member 252 may be positioned at the entrance ofthe temperature rising section 210 for blocking external air to preventheat loss of the post-processing apparatus 200. The second air curtainmember 254 may partition the temperature rising section 210 and the mainsection 220 for preventing interference between the temperature risingsection 210 and the main section 220 in terms of heat and light. Thethird air curtain member 256 may partition the main section 220 and thecooling section 230 for preventing interference between the main section220 and the cooling section 230 in terms of heat and light. The fourthair curtain member 258 may be positioned at the exit of the coolingsection 230 for blocking external air and assisting cooling of the solarcell 100.

As described above, in this embodiment of the present invention, thefirst to fourth air curtain members 252, 254, 256, and 258 are provided.However, the embodiments of the present invention are not limitedthereto. For example, only one of the first to fourth air curtainmembers 252, 254, 256, and 258 may be provided. In addition, one or moreadditional air curtain members may be further provided at positionsdifferent from those of the first to fourth air curtain members 252,254, 256, and 258.

Hereinafter, the operation of the post-processing apparatus 200 with theabove-stated construction will be described in detail. A solar cell 100,which will pass through the main processing process (ST56) of thepost-processing operation (S50), is placed on the conveyor belt 202, andthen the conveyor belt 202 is sequentially moved through the temperaturerising section 210, the main section 220, and the cooling section 230.In the temperature rising section 210, the solar cell 100 ispreliminarily heated to a temperature necessary for the main period(ST562) by the heat source unit 214. In the main section 220, the lightsource unit 222 emits light to the solar cell 100, and the heat sourceunit 224 supplies heat to the solar cell 100 to passivate the surface ofthe semiconductor substrate 110 or the bulk of the semiconductorsubstrate 110 (e.g. H⁺ is converted into H⁰ or H⁻ to generate the B-Hcombination). In the cooling section 230, the solar cell 100 is cooled.

In the main section 220, the light source unit 222 emits light havinglight intensity necessary for the main period (ST562), and the heatsource unit 224 maintains the solar cell 100 at a temperature necessaryfor the main period (ST562). In addition, the moving speed of theconveyor belt 202 may be adjusted such that the solar cell 100 can stayin the main section 220 for a desired process time. As a result, themain processing process (ST56) may be carried out on the solar cell 100based on heat treatment temperature, light intensity, and process timesatisfying the conditions of Equations 1 to 15.

That is, in the post-processing apparatus 200 according to thisembodiment of the present invention, the main processing process (ST56)of the post-processing operation (S50) for supplying both heat and lightmay be stably and efficiently carried out to post-process thesemiconductor substrate 110 or the solar cell including thesemiconductor substrate 110, temperature, light intensity, and processtime necessary for the main processing process (ST56) of thepost-processing operation (S50) may be maintained to maximize theeffects of the main processing process (ST56).

The post-processing apparatus 200 may post-process the solar cell 100 ina stand-alone fashion in which the solar cell 100 is post-processedafter the electrode forming operation (ST40) (see FIG. 3).Alternatively, the post-processing apparatus 200 may sequentially carryout a portion or the entirety of the electrode forming operation (ST40)(specifically, the firing operation (ST44) and/or the hydrogen diffusionprocess (ST52)) and the preliminary heat treatment process (ST54).Alternatively, the post-processing apparatus 200 may control operationsof the light source unit 22 and the heat source units 214 and 224 suchthat a portion or the entirety of the electrode forming operation (ST40)(specifically, the firing operation (ST44) and/or the hydrogen diffusionprocess (ST52)) and the preliminary heat treatment process (ST54) areall carried out in the post-processing apparatus 200. Various othermodifications are also possible.

In the above-described embodiment of the present invention, the in-lineprocess using the conveyer belt 202 is carried out, and the atmosphericheating is used in the temperature rising section 210 and the mainsection 220. However, the embodiments of the present invention are notlimited thereto. Hereinafter, a modification of the post-processingapparatus 200 will be described in detail with reference to FIG. 13.

FIG. 13 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to a modification ofthe embodiments of the present invention. FIG. 14 is a view showing anexample of a worktable applied to the post-processing apparatus of thesolar cell shown in FIG. 13. (a) of FIG. 14 is a plan view schematicallyshowing the worktable, (b) of FIG. 14 is a partial perspective viewshowing first and second parts, and (c) FIG. 14 is a partial perspectiveview showing a state in which solar cells are positioned on the firstand second parts. Parts identical to or similar to those of thepost-processing apparatus according to the previous embodiment of thepresent invention may be equally applied to the following embodiments ofthe present invention, and therefore a detailed description thereof willbe omitted.

As shown in FIG. 13, in this modification, no conveyor belt ispositioned in the temperature rising section 210, the main section 220,and the cooling section 230, and the process is carried out in a statein which the solar cell 100 is stationary. When the process iscompleted, the solar cell 100 may be moved by a worker or a transferdevice, such as a working beam. That is, the solar cell 100 may bepreliminarily heated in a state in which the solar cell 100 ispositioned in the temperature rising section 210. When the preliminaryheating process is completed, the solar cell 100 positioned in thetemperature rising section 210 may be moved into the main section 220.When the process is completed in the main section 220, the solar cell100 positioned in the main section 220 may be moved into the coolingsection 230.

That is, in this embodiment of the present invention, thepost-processing apparatus 200 has a batch structure in which the processis carried out in a state in which the solar cell 100 is stationary. Inan instance in which the process is carried out in a state in which thesolar cell 100 is stationary as described above, it is possible toeasily adjust and maintain light intensity and thermal energy requiredfor the temperature rising section 210, the main section 220, and thecooling section 230 and to easily adjust process time. In addition,interference with an external environment may be minimized during theprocess, thereby improving uniformity of the process. Furthermore, theconveyor belt may be omitted, thereby reducing facility costs.

In this embodiment of the present invention, the temperature risingsection 210, the main section 220, and the cooling section 230 are allpositioned in one chamber 208. In an instance in which the temperaturerising section 210, the main section 220, and the cooling section 230are all positioned in one chamber 208 as described above, aninstallation space for the temperature rising section 210, the mainsection 220, and the cooling section 230 may be minimized.

For example, a support table 206 for supporting the solar cell 100 maybe positioned in the temperature rising section 210, the main section220, and the cooling section 230. The support table 206 may have amaterial or structure which does not interrupt the supply of thermalenergy from the heat source units 214 and 224 to the solar cell 100.However, the embodiments of the present invention are not limitedthereto. Another structure for fixing the solar cell 100 may be providedinstead of the support table 206.

Solar cells 100 may be individually placed on the support table 206 andindividually moved. Alternatively, as shown in FIG. 14, a plurality ofsolar cells 100 may be placed on a worktable (tray) 204, and then theworktable 204 may be placed on the support table 206. In this case, itis possible to simultaneously move a large number of solar cells 100,thereby improving process efficiency.

In this embodiment of the present invention, the solar cells 100 may beplaced on the worktable 204 in a state in which interference with thelight source unit 222 positioned at the upper side of the worktable 204and interference with the heat source units 214 and 224 positioned atthe lower side of the worktable 204 are minimized.

For example, the worktable 204 may include a frame part 204 a forming anouter edge of the worktable 204, a plurality of first parts 204 bextending in one direction at uniform intervals, and a plurality ofsecond parts 204 c extending in a direction intersecting the first parts204 b at uniform intervals.

The first parts 204 b and the second parts 204 c intersect each other inthe frame part 204 a. As a result, the worktable 204 has a matrix ormesh structure. More specifically, a space S (e.g. a quadrangular space)is defined by two neighboring first parts 204 b and two neighboringsecond parts 204 c. The side of the space S is blocked by the firstparts 204 b and the second parts 204 c. Consequently, the space S may beformed in the shape of a closed opening when viewed from above. In thefigure, the first parts 204 b and the second parts 204 c are illustratedas each having a straight shape and being coupled to each other.However, the embodiments of the present invention are not limitedthereto. For example, the first parts 204 b and the second parts 204 cmay have a single structure including one layer. Various othermodifications are also possible.

In this embodiment of the present invention, the edge of each solar cell100 is placed on two neighboring first parts 204 b and two neighboringsecond parts 204 c. That is, the vertical width of each solar cell 100may be less than the width of the two neighboring first parts 204 b, andthe horizontal width of each solar cell 100 may be less than the widthof the two neighboring second parts 204 c. Consequently, the area of thespace S is less than that of each solar cell 100 with the result thatthe edge of each solar cell 100 is placed over the first and secondparts 204 b and 204 c. That is, each solar cell 100 is placed over thespace S defined by the two neighboring first parts 204 b and the twoneighboring second parts 204 c while entirely covering the space S. As aresult, thermal energy from the heat source units 214 and 224 positionedat the lower side of the worktable 204 may be effectively transferred tothe solar cell 100 through the space S. On the other hand, light fromthe light source unit 222 at the upper side of the worktable 204 may beblocked by the worktable 204 and the solar cell 100 with the result thatthe heat source units 214 and 224 are prevented from being affected bythe light from the light source unit 222. Consequently, it is possibleto prevent lowering in temperature uniformity of the solar cell 100 dueto interference between the light source unit 222 and the heat sourceunits 214 and 224.

In the embodiment shown in FIG. 14, the edge of each solar cell 100 isplaced over the first and second parts 204 b and 204 c. However, theembodiments of the present invention are not limited thereto. Theworktable 204 may have various structures for fixing the solar cell 100.In another modification, as shown in FIG. 15, the vertical width of eachsolar cell 100 may be equal to the width of two neighboring first parts204 b, and the horizontal width of each solar cell 100 may be equal tothe width of two neighboring second parts 204 c. In addition,protrusions P may protrude inwardly from the first and second parts 204b and 204 c for each space S such that each solar cell 100 is placed onthe protrusions P. As a result, a major portion of the area of the solarcell 100 excluding portions corresponding to the protrusions P may beplaced over the space C, thereby effectively achieving heat transfer. Asshown in (a) of FIG. 15, the protrusions P may be provided at the firstand second parts 204 b and 204 c on four corners of each space S.Alternatively, as shown in (b) of FIG. 15, the protrusions P may beprovided at the first and second parts 204 b and 204 c on the middleparts of four sides of each space S. The position and number of theprotrusions P may be variously changed.

Referring back to FIG. 14, a plurality of spaces S may be defined by thefirst parts 204 b and the second parts 204 c. Consequently, acorresponding number of solar cells 100 may be placed on the worktable204. For example, 10 to 20 spaces S may be formed in one direction (e.g.a horizontal direction), and 10 to 20 spaces S may be formed in anotherdirection (e.g. a vertical direction) intersecting the above-mentioneddirection. As a result, 100 to 400 spaces S may be formed on eachworktable 204. Consequently, 100 to 400 solar cells 100 may besimultaneously processed on one worktable 204, thereby simplifying theprocess and achieving mass production.

The strength of the work table 204 may be increased by the provision ofthe frame part 204 a, thereby improving structural stability of the worktable 204. For example, the width of the frame part 204 a may be greaterthan that of the first and second parts 204 b and 204 c to furtherincrease the strength of the work table 204. However, the embodiments ofthe present invention are not limited thereto. The width of the framepart 204 a may be variously changed. In addition, the frame part 204 amay be omitted to simplify the structure of the work table 204.

In this embodiment of the present invention, the material of the framepart 204 a may be different from that of the first and second parts 204b and 204 c. For example, the material of the frame part 204 a may havea higher strength than that of the first and second parts 204 b and 204c. In this case, the strength of the work table 204 may be increased. Inaddition, the material of the first and second parts 204 b and 204 c mayhave a higher thermal conductivity than that of the frame part 204 a. Inthis case, transfer of heat from the heat source units 214 and 224 tothe solar cell 100 may not be interrupted. For example, the frame part204 a may be made of stainless steel (SUS), and the first and secondparts 204 b and 204 c may be made of aluminum. However, the embodimentsof the present invention are not limited thereto. The frame part 204 aand the first and second parts 204 b and 204 c may be made of variousother materials.

FIG. 16 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to anothermodification of the embodiments of the present invention. Partsidentical to or similar to those of the post-processing apparatusaccording to the previous embodiment of the embodiments of the presentinvention may be equally applied to the following embodiments of thepresent invention, and therefore a detailed description thereof will beomitted.

Referring to FIG. 16, in this embodiment of the present invention, thepost-processing apparatus 200 has a batch structure in a state in whicha temperature rising section 210, a main section 220, and a coolingsection 230 have separate spaces. Consequently, it is possible to easilyadjust and maintain light intensity and thermal energy required for thetemperature rising section 210, the main section 220, and the coolingsection 230 and to easily adjust process time. In addition, interferencewith an external environment may be minimized during the process,thereby improving uniformity of the process. Furthermore, no conveyorbelt may be provided, thereby reducing facility costs.

However, the embodiments of the present invention are not limitedthereto. For example, the temperature rising section 210 and the mainsection 220 may be continuously positioned such that the process can becarried out based on an in-line process, and the cooling section 230 mayhave a separate structure. In another example, the temperature risingsection 210 may have a separate structure, and the main section 220 andthe cooling section 230 may be continuously positioned such that theprocess can be carried out based on the in-line process. In anotherexample, the temperature rising section 210 and the main section 220 mayhave a batch structure in a state in which the temperature risingsection 210 and the main section 220 are positioned in one chamber, andthe cooling section 230 may have a separate structure. In a furtherexample, the temperature rising section 210 may have a separatestructure, and the main section 220 and the cooling section 230 may havea batch structure in a state in which the main section 220 and thecooling section 230 are positioned in one chamber. Various othermodifications are also possible.

In this embodiment of the present invention, a work table 204, on whicha solar cell 100 is placed, may be preliminarily heated or heat-treatedin a state in which the work table 204 is in contact with a heat sourceunit 214 of the temperature rising section 210 or a heat source unit 224of the main section 220. As a result, heat from the work table 204 istransferred to the solar cell 100 by conduction.

In an instance in which the heat from the work table 204 is transferredto the solar cell 100 by conduction as described above, it is possibleto heat the solar cell 100 within a short time. In addition, the processis carried out in a state in which the solar cell 100 is stationary inthe temperature rising section 210 and the main section 220.Consequently, it is possible to easily adjust time during which lightand heat are supplied to the solar cell 100 by adjusting time duringwhich the solar cell 100 stays in the temperature rising section 210 orthe main section 220. In addition, it is possible to carry out theprocess for a desired process time without increasing the size of thetemperature rising section 210 and the main section 220.

In the figure, the temperature rising section 210 is illustrated asincluding an additional heat source unit 216 for carrying outatmospheric heating by radiation to improve heating efficiency. However,the embodiments of the present invention are not limited thereto. Theadditional heat source unit 216 may not be provided. Various othermodifications are also possible.

However, the embodiments of the present invention are not limitedthereto. For example, the work table 204, on which the solar cell 100 isplaced, may be preliminarily heated or heat-treated in a state in whichthe work table 204 is spaced apart from the heat source unit 214 of thetemperature rising section 210 or the heat source unit 224 of the mainsection 220. In this case, heat is transferred to the solar cell 100 byradiation. Consequently, it is possible to stably supply heat to thesolar cell 100 while minimizing possible damage to the solar cell 100.

FIG. 17 is a view schematically showing the structure of apost-processing apparatus of a solar cell according to anothermodification of the embodiments of the present invention.

Referring to FIG. 17, in this embodiment of the present invention, thepost-processing apparatus 200 may include a plurality of post-processingunits, each of which includes a temperature rising section 210, a mainsection 220, and a cooling section 230. For example, one post-processingunit including a temperature rising section 210, a main section 220, anda cooling section 230 may be positioned above another post-processingunit including a temperature rising section 210, a main section 220, anda cooling section 230. That is, a plurality of post-processing units maybe positioned in a vertical direction to have a multi-stage structure,thereby improving productivity while minimizing an installation space.

Each post-processing unit of the post-processing apparatus 200 shown inFIG. 17 has the same structure as the post-processing apparatus 200shown in FIG. 13. However, the embodiments of the present invention arenot limited thereto. For example, each post-processing unit of thepost-processing apparatus 200 shown in FIG. 17 has the same structure asthe post-processing apparatus 200 shown in FIG. 12 or 16. Various othermodifications are also possible.

FIG. 18 is a view schematically showing the structure of a light sourceunit applicable to a post-processing apparatus of a solar cell accordingto a further modification of the embodiments of the present invention.

Referring to FIG. 18, in this embodiment of the present invention, theouter surface of a cover substrate 223 (i.e. the surface of the coversubstrate 223 opposite to a solar cell 100 (see FIG. 12)) may be convexto the solar cell 100. As a result, light may be more uniformly suppliedto the solar cell 100 through the cover substrate 223 such that thelight can be more uniformly distributed over the solar cell 100. Theouter surface of the cover substrate 223 may be variously convex. Forexample, the cover substrate 223 may include a base substrate 223 a (seeFIG. 12) which is convex outward and a plurality of layers 223 b (seeFIG. 12), positioned on the base substrate 223 a, having differentrefractive indices. As a result, the cover substrate 223 may be convexoutward. Various other modifications are also possible. On the otherhand, a light source of a general plasma lighting system is usedoutside. For this reason, an outwardly concave cover substrate isgenerally used to improve straightness of light.

As is apparent from the above description, it is possible for thepost-processing apparatus according to the embodiments of the presentinvention to stably and efficiently carry out the post-processingoperation for supplying both heat and light so as to post-process thesolar cell and to maintain temperature, light intensity, and processtime necessary for the post-processing operation, thereby maximizing theeffects of the main processing process.

The above described features, configurations, effects, and the like areincluded in at least one of the embodiments of the present invention,and should not be limited to only one embodiment. In addition, thefeatures, configurations, effects, and the like as illustrated in eachembodiment may be implemented with regard to other embodiments as theyare combined with one another or modified by those skilled in the art.Thus, content related to these combinations and modifications should beconstrued as included in the scope and spirit of the invention asdisclosed in the accompanying claims.

What is claimed is:
 1. A post-processing apparatus of a solar cell thatcarries out a post-processing operation including a main period forheat-treating a solar cell having a semiconductor substrate whileproviding light to the solar cell, the post-processing apparatuscomprising: a main section to carry out the main period, wherein themain section comprises a first heat source unit to provide heat to thesemiconductor substrate and a light source unit to provide light to thesemiconductor substrate, the first heat source unit and the light sourceunit being positioned in the main section, and the light source unitcomprises a light source constituted by a plasma lighting system (PLS).2. The post-processing apparatus according to claim 1, wherein lightprovided to the semiconductor substrate by the light source has awavelength of 600 nm to 1000 nm.
 3. The post-processing apparatusaccording to claim 1, wherein the light source is provided at a lightemitting surface thereof with a cover substrate comprising a basesubstrate and a plurality of layers positioned on the base substrate,the plurality of layers comprising oxides having different refractiveindices.
 4. The post-processing apparatus according to claim 1, whereinthe light source unit and the first heat source unit respectivelyprovide light and heat to the semiconductor substrate in a state inwhich the light source unit and the first heat source unit are spacedapart from each other.
 5. The post-processing apparatus according toclaim 1, further comprising: a temperature rising section to carry out atemperature rising period for preliminarily heating the semiconductorsubstrate, the temperature rising period being carried out before themain period, wherein the temperature rising section comprises a secondheat source unit to preliminarily heat the semiconductor substrate, thesecond heat source unit being positioned in the temperature risingsection.
 6. The post-processing apparatus according to claim 5, furthercomprising an additional heat source unit positioned at an entrance ofthe temperature rising section such that the additional heat source unitis opposite to the second heat source unit.
 7. The post-processingapparatus according to claim 1, further comprising a cooling section tocarry out a cooling period for cooling the semiconductor substrate, thecooling period being carried out after the main period.
 8. Thepost-processing apparatus according to claim 1, further comprising: atemperature rising section to carry out a temperature rising period forpreliminarily heating the semiconductor substrate, the temperaturerising period being carried out before the main period; a coolingsection to carry out a cooling period for cooling the semiconductorsubstrate, the cooling period being carried out after the main period;and a conveyor belt passing though the temperature rising section, themain section, and the cooling section, and the solar cell being placedon the conveyor belt, wherein the temperature rising period, the mainperiod, and the cooling period are carried out based on an in-lineprocess.
 9. The post-processing apparatus according to claim 8, furthercomprising a partition wall unit positioned at at least one of a spacedefined between the temperature rising section and the main section forpartitioning the temperature rising section and the main section, and aspace defined between the main section and the cooling section forpartitioning the main section and the cooling section.
 10. Thepost-processing apparatus according to claim 8, wherein at least one ofthe temperature rising section and the cooling section further comprisean additional light source positioned adjacent to the main section. 11.The post-processing apparatus according to claim 8, further comprising:an air curtain member positioned at at least one of an entrance of thetemperature rising section, a space defined between the temperaturerising section and the main section, a space defined between the mainsection and the cooling section, and an exit of the cooling section. 12.The post-processing apparatus according to claim 1, further comprising:a temperature rising section to carry out a temperature rising periodfor preliminarily heating the semiconductor substrate, the temperaturerising period being carried out before the main period; and a coolingsection to carry out a cooling period for cooling the semiconductorsubstrate, the cooling period being carried out after the main period,wherein the temperature rising section, the main section, and thecooling section have a batch structure in which a process is carried outin a state in which the solar cell is stationary.
 13. Thepost-processing apparatus according to claim 1, wherein the solar cellis placed on a conveyor belt or a work table, and the conveyor belt orthe work table has a mesh structure.
 14. The post-processing apparatusaccording to claim 1, wherein the main section has a temperature of 100to 800° C., and the main section has temperature and light intensitysatisfying Equation 1 and light intensity and process time satisfyingEquations 2 to 5.1750−31.8·T+(0.16)·T ² ≤I≤10⁵  <Equation 1>1.7×10² ≤I<10³, and P _(min)=13000−(31.7)·1+(0.02)·(I)²≤P≤10000  <Equation 2>10³ ≤I<10⁴, and 1030−(0.25)·I+(1.5×10⁻⁵)·(I)² ≤P≤10000  <Equation 3>10⁴ ≤I≤5×10⁴, and 35.5−(0.0012)·I+(10⁻⁸)·(I)² ≤P≤10000  <Equation 4>5×10⁴ ≤I≤10⁵, and 0.5≤P≤10000  <Equation 5> where T is temperate (° C.)of the main section, I is light intensity (mW/cm²) of the main section,and P is process time (sec) of the main section.